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U.  S.  :  MT  OF  AGRICULTURE, 

BURKAF  ov  CHEMISTRY— BULLETIN  No.  14& 

\N  ILKY.  CHIBP  or  BUBKAV. 


RECAP 


IPTE  TOXTOTTY  OF  CAFFEIN: 

AN  EXl^ERIMENTAL  STUDY 

().\    I'il'FERENT  SPEClfes  OF  ANIMALS. 


BY 


WHiLLLM  S.\LANT, 

Chief  rharniucologicnl  Lnfjoralonj,  D-iviMon  of  Drugs , 

AND 

J.  B.  RIEGER, 

Assistant  f^- ,-"'-' 


"'^i^^l^^^ 


GOVERNMENT  PRINTING  OPPIOE. 


ja^SiiXi 


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Columbm  ®nitJers(ttp 
intljeCttpoflfttigork 

College  of  ^fjpsiciansf  anb  ^urgeonsf 
Hifararp 


1ksik-<1  April  1,  1'J12. 


U.  S.  DEPARTMENT  OE  AGRICULTURE. 

BUREAU  OF  CHEMISTRY— BULLETIN  No.  148. 


H.  w.  WILKY,  t;HiKF  OK  Bureau. 


THE  TOXICITY  OF  CAFFEIN: 

AN  EXPERIMENTAL  STUDY 

ON  DIFFERENT  SPECIES  OF  ANIMALS. 


WILLIA.M  SALAXT, 

Chief  Pharmacological  Laboratory,  Division  of  Drugs, 

AND 

J.  B.  RIEGER, 

Assistant  Chemist. 


WASHINGTON: 

GOVERNMENT  PRINTING  OPPIOE. 

1912. 


LEHER  OF  TRANSMITTAL, 


U.  S.  Department  of  Agriculture, 

Bureau  of  Chemistry, 
Washington,  D.  C,  November  1 4, 1911. 
Sir:  I  have  the  honor  to  submit  for  your  approval  a  manuscript 
on  the  toxicity  of  caffein,  which  is  the  first  of  a  series  of  reports  to 
be  made  by  Dr.  Salant  on  the  pharmacology  of  this  drug;  the  con- 
clusions here  reported  are,  therefore,  in  some  particulars  to  be 
regarded  as  tentative.  The  data  obtained  are  primarily  of  use  in  the 
execution  of  the  food  and  drugs  act,  but  are  capable  of  much  broader 
apphcation. 

Acknowledgment  is  made  of  the  assistance  rendered  by  Dr.  John 
R.  Mohler,  Cliief  of  the  Pathological  Division,  Bureau  of  Animal 
Industry,  and  his  assistants,  in  performing  the  autopsies  recorded  in 
this  report.  I  recommend  the  publication  of  the  manuscript  as 
Bulletin  No.  148  of  the  Bureau  of  Chemistry. 
Respectfully, 

H.  W.  Wiley,  Chief. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 


nPHIS  PUBLICATION  may  be  pro- 

-*-     cured  from  the  Superintendent  of 

Doctunente,  Government  Printing  Office 

Washinglon,  D.  C,  at  15  cents  per  copy 


CONTENTS. 


Pago. 

Tiilroduction 5 

Historical  review  of  the  literature  on  the  toxicity  of  caffein 9 

Acute  caffein  intoxication 18 

Experiments  on  rabbitH 18 

Subcutaneous  injection 18 

Administration  by  mouth 2G 

Injection  into  the  peritoneal  cavity 28 

Intramuscular  injection 33 

Intravenous  injection 37 

Summary 42 

Experiments  on  guinea  pigs 43 

Subcutaneous  injection 43 

Injection  into  the  peritoneal  cavity 47 

Administration  by  mouth . .  49 

Summary '  52 

Experiments  on  cats 53 

Subcutaneous  injection 53 

Injection  into  the  peritoneal  cavity 56 

Administration  by  mouth 57 

Summary 59 

Experiments  on  dogs 60 

Administration  by  mouth 60 

Subcutaneous  injection 60 

Experiments  on  puppies 61 

Summary 62 

Chronic  caffein  intoxication 63 

Experiments  on  rabbits 63 

Experiments  on  dogs 75 

Discussion  of  results 91 

General  summary  and  conclusions 95 

Bibliography 97 

3 


THE  TOXICITY  OF  CAFFEIN. 


INTRODUCTION. 

Comparative  physiology  lias  established  the  fundamental  fact  that 
some  properties  are  common  to  all  forms  of  living  matter.  But  the 
same  method  of  inquiry  has  also  led  to  the  recognition  of  marked 
differences  in  the  physic^logical  processes  of  various  species  of  animals. 
Among  tlie  most  important  investigations  which  contributed  to  the 
knowledge  of  such  variation  of  function  are  the  studies  in  comparative 
metabolism.  It  is  now  recognized  that  metabolism  is  in  some 
resj^ects  cpiite  different  in  herbivora  and  in  carnivora.  Some  forms 
of  oxidation  are  much  greater  in  the  rabbit  than  in  cats  and  dogs. 
Nuclein  metabolism  presents  important  differences  in  the  rabbit  and  in 
man,  while  the  mode  of  neutralizing  acid  in  the  body  may  be  cited  as 
another  variation  in  the  metabohsm  of  these  forms.  Perhaps  the 
most  striking  examples  of  differences  in  the  metabolism  of  different 
organisms  is  furnished  by  the  results  of  studies  on  the  fate  of  certain 
poisons  introduced  into  the  body. 

The  classical  experiments  of  Bunge  and  Schmiedeberg^^  '^on  the  syn- 
thesis of  hippuric  acid  are  of  interest  in  this  regard.  It  will  be  recalled 
that  in  the  dog  the  synthesis  takes  place  in  the  kidney ;  the  rabbit  is  able 
to  form  hippuric  acid  in  the  liver  as  well  as  in  the  kidney,  while  frogs 
can  synthesize  hippuric  acid  even  when  both  of  these  organs  have  been 
removed  or  excluded  from  the  circulation.  Observations  on  the  fate 
of  some  of  the  alcohols  of  tlie  fatty  acid  series  have  likewise  s]lo^^^l  that 
these  substances  maybe  combined  with  glycuronic  acid  in  some  animals 
but  not  in  others.  According  to  Thierfelder  and  Von  Mering,  ^*  ter- 
tiary alcohols  are  combined  in  tliis  manner  in  the  rabbit  but  not  in  the 
dog.  According  to  Neubauer,®^  the  primary  and  secondary  alcohols 
are  so  combined  in  the  dog  as  well  as  in  tlie  rabbit,  but  to  a  greater 
degree  in  the  latter. 

Pohl  '^  found  that  amyl  alcohol  is  largely  eliminated  by  the  lungs  in 
the  cat  and  in  the  dog.  The  protocols  of  liis  experiments  show  that 
65  per  cent  of  the  alcohol  given  these  animals  was  thus  recovered, 
while  he  recovered  only  22  per  cent  of  this  substance  in  the  expired 
air  of  the  rabbit.  Examination  of  me  urine  showed  the  ])resence  of 
glycuronic  acid.     Hofmeister's  ^^  work  with  tellurium  in  the  dog  is  of 

a  The  small  Tigures  refer  to  the  bibliography  at  the  end  of  this  bulletin. 


6  THE   TOXICITY  OF   CAFFEIN. 

interest  in  this  connection.  He  made  the  important  discovery  that 
some  animals  possess  the  power  of  methylation  as  well  as  of  demethyl- 
ation.  Abderhalden  and  Brahm's  ^  experiments  with  pyridin  show 
that  the  same  is  true  of  young  dogs  when  on  a  meat  diet.  His  experi- 
ments on  rabbits  with  this  substance  were  negative. 

The  metabohsm  of  oaffein  and  theobromin  furnisli  another  illustra- 
tion of  differences  in  the  physiological  mechanism  of  animals.  Al- 
though the  substances  foutid  in  the  urine  of  man,  dog,  and  rabbit  after 
the  administration  of  caffein  and  theobromin  were  the  same,  the  quan- 
tities varied  considerably.  According  to  Krtiger  and  Schmidt,"  over 
14  per  cent  of  the  theobromin  introduced  into  the  rabbit  is  eliminated 
as  7-methyl  xanthin  in  the  urine.  The  dog  eliminates  only  about  0.67 
per  cent.  On  the  other  hand,  the  amount  of  tri-methyl  xanthin  elimi- 
nated was  only  3  per  cent  in  the  dog  and  not  quite  1  per  cent  in  the 
rabbit. 

It  appears,  therefore,  from  studies  in  comparative  metabolism, 
whether  endogenous  or  exogenous,  that  well-marked  physiologic  and 
chemical  differences  exist  in  various  species  of  animals.  That  phar- 
macological action  may  likewise  vary  in  different  species  of  animals 
is  shown  by  the  following  investigations.  According  to  Guinard,^^ 
who  made  an  exhaustive  study  of  morphin,  the  reaction  to  this  alka- 
loid varies  in  different  forms  of  life,  both  qualitatively  and  quanti- 
tatively. He  established  its  narcotic  effect  in  the  dog,  rabbit,  guinea 
pig,  white  mice,  and  rats,  while  for  the  cat,  horse,  ox,  sheep,  hog,  and 
goat  it  is,  on  the  contrary,  a  stimulant.  Moreover,  there  is  no  evi- 
dence of  cerebral  effect.  The  stimulating  effect  of  morphin  on  the 
nervous  system  in  some  animals  was  also  observed  by  Noe  ^^  in  experi- 
ments with  this  substance  on  the  hedgehog. 

Guinard  ^^-  ^°  has  also  shown  that  morphin  has  no  narcotic  effect  in 
the  marmot,  although  this  animal  is  very  sensitive  to  the  drug.  Two 
milligrams  per  kilo  were  found  to  be  a  surely  fatal  dose  for  this  animal. 
His  experiments  on  the  comparative  toxicity  of  morphin  ^"  ^^  show  a 
considerable  range  of  variation  in  different  species.  Thus  the  fatal 
dose  for  the  dog  was  found  to  be  0.65  per  kilo,  while  7  mg  per  kilo  is 
the  fatal  dose  for  the  horse.  About  twice  the  amount  is  fatal  for  the 
ox  and  0.2  mg  per  kilo  kills  the  pig.  Experiments  with  other  drugs  has 
shown  that  a  considerable  range  of  variation  in  resistance  exists  in 
animals  of  different  species. 

Noe's  "•''  studies  on  the  comparative  toxicity  of  chloral  brought  out 
the  interesting  fact  that  the  rabbit  is  more  resistant  to  it  than  the 
hedgehog  and  the  latter  more  resistant  than  the  guinea  pig.  Per- 
haps the  most  striking  example  of  a  difference  in  reaction  of  the 
same  substance  in  widely  different  species  is  that  furnished  by 
apocodein,  quinin,  and  yohimbin.     According  to  Gunn^^  these  sub- 


INTRODUCTION.  7 

stances  have  been  found  to  cause  vasodilation  in  warm-blooded 
animals,  but  they  constrict  the  blood  vessels  of  the  frog. 

Experiments  with  upomorjihin  likewise  show  that  the  reaction  to 
this  substance  varies  in  dillVrent  species  of  animals.  The  resistance 
of  the  cat  to  this  drug  is,  accortling  to  Guinard,^'  ten  times  greater  than 
that  of  the  dog,  and  the  latter  is  more  sensitive  than  the  rabbit  to 
the  ciystalline  form  of  apomorphin  when  given  intravenously. 
According  to  Robert  *■'  amygdalin  is  without  effect  on  dogs,  but  it 
is  poisonous  to  rabbits.  Lapicque  *"  found  that  the  toxicity  of 
curara  varies  in  different  species  of  frogs,  the  dose  required  to  pro- 
duce paralysis  in  Rana  esculenta  being  three  times  greater  than  in 
Bufo  vulgaris.  Weir  Mitchell  ^°  pointed  out  long  ago  that  turtles 
stand  enormous  doses  of  curara.  Sclimiedeberg's  experiments  with 
cafTein  on  Rana  temporaria  and  Rana  esculenta  (and  more  recently 
those  of  Jacobi  and  Golowinski  ^^  with  caffein,  theobromin,  and 
theophyllin)  are  also  of  interest  in  this  connection.  These  experi- 
menters observed  well-marked  differences  of  reaction  to  methyl- 
xanthins  in  these  closely  allied  forms. 

Experiments  with  quinin  have  shown  that  the  action  of  this  sub- 
stance differs  in  some  animals.  It  causes  a  fall  of  temperature  imme- 
diately after  its  administration  in  the  guinea  pig,  but  frequently 
produces,  at  first,  a  rise  of  temperature,  followed  by  an  unimportant 
fall,  in  rabbits,  dogs,  and  man. 

The  numerous  investigations  which  have  been  carried  out  on  the 
effect  of  atoxyl  within  recent  years  have  contributed  much  to  the 
comparative  pharmacology  of  this  substance.  Although  the  symp- 
toms and  organic  changes  produced  by  this  substance  in  a  variety  of 
animals  present  no  great  differences,  the  resistance  of  some  has  been 
found  to  vary;  according  to  Koster**'  it  is  more  toxic  for  dogs  than 
for  rabbits.  A  number  of  other  substances  have  been  found  by 
various  experimenters  to  vary  in  toxicity  for  dift'erent  species  of 
animals.  Cantharadin,  phenol,  atropin,  and  strychnin  may  be  men- 
tioned as  illustrations. 

Pharmacological  studies  on  lower  forms  of  life  have  also  revealed 
marked  variations  in  the  effect  of  some  poisons.  Observations  made 
by  Danilewski/^  with  hydrochinone  indicate  that  solutions  of  1  to 
100  or  200  are  toxic  to  Celentrates,  causing  paralysis  in  these  organ- 
isms. Echinoderms  are  killed  within  one  or  two  hours  in  1  to  1,000 
or  2,000  solution,  while  in  Vermes  even  weaker  solutions  cause 
tetanus  and  finally  paralysis.  The  experiments  of  Drzewina^®  with 
potassium  cyanid  are  also  interesting  in  this  connection.  Teleosts 
placed  in  100  cc  of  sea  water  containing  twentieth-normal  potassium 
cyanid  showed  signs  of  asphyxia  and  died  in  10  to  20  minutes. 
Actinia  placed  in  a  solution  of  sea  water  containing  five  times  as 
much  potassium  cyanid  were  active  on  the  thirteenth  day  of  the 


8  THE   TOXICITY   OF   CAFFEIN. 

experiment.  Similar  results  were  obtained  with  other  marine 
organisms. 

From  these  data  it  is  evident  that  the  toxicity  of  a  substance  may 
vary  considerably  in  different  forms  of  life.  It  has  been  shown  also 
by  some  investigations  cited  by  Salant^^  that  the  action  of  drugs 
may  be  modified  by  different  conditions  in  the  environment  as  well 
as  in  the  subject  of  the  experiment.  The  recognition  of  the  import- 
ance of  these  factors  in  determining  pharmacological  action  has  con- 
tributed much  to  the  elucidation  of  the  mechanism  by  which  drugs 
and  other  substances  produce  physiological  effects  in  the  body.  More- 
over, such  knowledge  has  often  enhanced  the  therapeutic  value  of 
pharmaco-dynamic  agents  and  has  frequently  served  to  avert  effects 
of  an  undesirable  character  in  man  and  domestic  animals.  The  results 
obtained  in  one  species  of  animals  under  a  particular  condition  do  not 
admit,  therefore,  of  universal  application.  Furthermore,  the  nature 
of  the  action  of  a  drug  can  only  be  partly  learned  from  the  manifes- 
tation of  its  acute  effects.  Equally  important,  therefore,  especially  in 
studies  on  toxicity,  are  the  changes  produced  in  chronic  intoxication. 

That  the  acute  effects  of  a  substance  can  hardly  be  considered  a 
correct  estimate  of  its  toxicity  is  shown  by  the  evidence  obtained  in 
experiments  on  tolerance  and  cumulative  action  of  drugs;  for  the 
toxicity  of  a  substance  may  diminish  when  the  substance  is  given 
steadily  for  a  long  time  if  the  body  acquires  tolerance  for  it.  Arsenic, 
morpliin,  and  cannabis  indica  may  be  cited  as  illustrations  of  drugs, 
the  toxicity  of  wliich  decreases  with  repeated  doses,  wliile  digitalis 
and  lead  show  a  tendency  to  increased  toxicity  when  similarly 
administered.  Moreover  the  acute  and  chronic  effects  are  sometimes 
qualitatively  different.  According  to  Igersheimer  *^  the  symptoms 
in  acute  atoxyl  intoxication  are  nausea,  vomiting,  and  diarrhea. 
These  symptoms  are  absent  in  clironic  intoxication,  in  wliich  trophic 
disturbances  of  the  skin  and  inflammation  of  the  mucous  membranes 
were  the  effects  produced.  That  the  acute  action  of  atoxyl  differs 
from  the  chronic  effects  was  likewise  shown  by  experiments  on  ani- 
mals. The  studies  of  von  Anrep  ^  on  cln-onic  atropin  intoxication 
are  of  interest  in  tliis  connection,  as  he  found  that  after  10  to  15 
injections  of  atropin  there  is  no  manifestation  of  symptoms  such  as 
is  observed  in  acute  intoxication,  while  the  effects  on  the  circulation 
are  also  less  marked,  the  acceleration  of  the  pulse  being  less  than 
after  the  same  dose  in  a  normal  subject  not  accustomed  to  its  use. 
Wlien  the  administration  of  atropin  is  continued  for  a  longer  time 
its  usual  effects  on  the  pulse  disappear  altogether;  there  is,  on  the 
contrary  a  decreased  frequency  of  the  pulse.  If  atropin  has  been 
administered  for  from  two  to  three  weeks,  respiration  is  likewise 
affected. 


HISTORICAL  REVIEW.  9 

mSTORICAI  REVIEW  OF  THE  LITERATURE  ON  THE  TOXICITY 

OF  CAFFEIN. 

CafFein  was  discovered  in  1820  by  Runge,"  Pelletier,"'  and  Robi- 
quet  '*  and  was  first  analyzed  by  Dumas  and  Pellctier,^"  but  its 
exact  percentixge  composition  was  detemiined  by  Pfaff  and  Liebig, 
71.  72  ^vhile  to  Herzog  *^'  "  belongs  the  cre<lit  of  having  esta])lished 
that  it  is  basic.  Strecker  ^-  prepared  caffein  synthetically  by  lieating 
theobromin  silver  and  methyl  iodid  in  a  closed  tube  for  24  hours. 
Soon  after  its  discovery  in  coffee  Oudry  "  reported  the  presence  of 
a  substance  in  tea  wliich  he  called  "thein."  Its  identity  with  cafTein 
was  established  15  years  later  by  Jol)st  ""^  and  also  by  Mulder.  ^-'  ®^ 
According  to  Brill/^  Mulder  (1838)  was  also  the  first  to  perform 
experiments  with  caffein  on  animals.  After  the  administration  of 
one-half  grain  to  a  j^regnant  rabbit  he  observed  loss  of  appetite  and 
ky}:)hosis.  The  rabbit  aborted  but  recovered  from  the  effects  of 
caffein.  It  has  since  been  made  the  subject  of  numerous  investiga- 
tions which  were  carried  out  on  a  variety  of  animals.  Observations 
with  caffein  were  also  made  on  the  human  subject.  About  four 
years  after  Mulder  pubhslied  his  results,  Lehmann  *^  (1842)  rei)orted 
experiments  on  a  number  of  people  who  were  given  caffein.  The 
administration  of  fi-om  2  to  10  gi'ains  of  the  alkaloid  was  followed  bv 
headache,  palpitation  of  the  heart,  increased  frequency  and  irregu- 
larity of  the  pulse,  tinnitus  aurium,  photopsia,  insomnia,  and  even 
dehrium.  Similar  experiments  reported  by  Frerichs  "  (1846)  indi- 
cate that  in  doses  of  25  grains  it  may  induce  severe  symptoms  about 
15  minutes  after  its  administration.  He  also  observed  circulatory  as 
well  as  nerv'ous  symptoms  and  vomiting. 

According  to  Albers  -  (1852),  4.5  grains  of  caffein  citrate  injected 
subcutaneously  into  the  thigh  of  a  rabbit  was  soon  followed  by  dimin- 
islied  motion  and  tremors  of  the  operated  thigh.  Other  symptoms 
reported  were  spasms  of  the  facial  muscles,  increased  resj)iratory 
movements,  and  mental  confusion.  Of  interest  in  this  connection 
are  tlie  experiments  of  Cogswell^^  (1852)  on  frogs.  He  concluded  that 
in  point  of  destructive  action  on  the  tissues,  caffein  is  far  superior 
to  morphin  and  may  be  compared  to  stryclmin  and  coniin,  its  action 
on  the  nervous  system  he  beheved  to  be  principally  confined  to  the 
effect  on  the  brain  and  spinal  cord. 

Lehmann"  (1853)  observed  increased  frequenc}^  of  heart  action 
after  the  acUninistration  of  4  grains,  wliich  were  given  with  a  normal 
diet  to  an  adult  man.  Wlien  the  dose  was  doubled  the  frequency  of 
the  pulse  was  stiU  more  increased,  heart  action  became  stronger,  and 
tremors  and  confusion  of  thought  with  excitement  of  the  imagination 
made  their  appearance.  There  was  also  an  increased  desire  to 
niicturate. 


10  THE   TOXICITY   OF   CAFFEIN". 

Stuhlmann  and  Falck  ^^  (1857)  were  the  first  to  make  a  study  of 
the  toxicity  of  caffein  on  animals  of  different  species.  The  adminis- 
tration of  0.5  gram  of  caffein  subcutaneously  or  per  rectum  in  rabbits 
induced  tremors,  tonic  and  clonic  convulsions,  paralysis,  and  increased 
frequency  of  respiration  at  first  followed  by  violent  dyspnoea.  On 
autopsy  he  noticed  congestion  of  the  organs  and  in  two  of  the  three 
rabbits  experimented  upon  punctiform  hemorrhages  of  the  brain  with 
congestion  of  the  meninges  were  found.  In  the  other  rabbit  anemia 
of  the  brain  was  observed.  Experiments  on  cats  were  carried  out 
by  subcutaneous,  intravenous,  and  rectal  injections.  The  symptoms 
observed  after  the  administration  of  0.5  -to  0.7  gram  of  caffein  were 
the  same  as  in  rabbits  except  that  the  cats  developed  diarrhea  when 
caffein  was  given  and  no  anatomic  lesions  were  found  on  autopsy. 
The  effect  of  caffein  on  dogs  indicated  that  in  subjects  of  medium 
weight  a  dose  of  0.5  gram  given  by  mouth  might  produce  restlessness 
and  increased  frequency  of  respiration,  while  the  injection  of  the 
same  amount  intravenously  into  such  animals  may  cause  death. 
Large,  full-growm  dogs,  however,  survived  an  intravenous  injection 
of  2  grams  of  caffein,  showing  symptoms  of  incoordination,  salivation, 
and  frequent  defecation.  These  investigators  also  made  observations 
on  caffein,  using  pigeons  and  other  birds;  0.5  to  0.1  gram  introduced 
into  the  stomach  caused  vomiting,  diarrhea,  tonic,  but  more  fre- 
quently clonic,  convulsions,  incoordination,  tremors,  paresis,  and 
paralysis. 

In  a  few,  but  not  in  all  of  the  birds,  there  was  at  first  increased 
frequency  of  respiration  followed  by  dyspnoea  and  circulatory  dis- 
turbances. These  amounts  of  caffein  proved  fatal  in  all  of  the  experi- 
ments on  birds.  Inflammation  of  the  intestinal  mucosa  and  conges- 
tion of  the  meninges  were  the  only  changes  found  on  autopsy. 
Stuhlmann  and  Falck  also  studied  the  effects  of  caffein  on  fishes  and 
toads.  Mitscherlich  ""^  (1858)  fed  0.4  gram  of  caffein  with  bread  to  a 
rabbit  and  noticed  lowered  temperature,  fatigue,  convulsions,  first 
increased  then  decreased  frequency  of  respiration,  and  on  autopsy 
congestion  of  all  the  viscera.  He  also  reported  observations  on  two 
frogs,  one  of  which  was  given  one-sixteenth  of  a  grain  of  caffein  in  a 
pill  with  bread.  It  was  administered  to  the  other  frog  in  aqueous 
solution,  but  the  mode  of  administration  was  not  published.  The 
symptoms  observed  were  in  the  main  the  same  as  in  rabbits.  In 
pigeons  0.125  gram  introduced  into  the  stomach  caused  severe  vomit- 
ing, muscular  incoordination,  tonic  rigidity  of  the  limbs,  and  retrac- 
tion of  the  head.  Respiration  was  increased  in  frequency.  Death 
followed  within  3  hours  and  15  minutes. 

From  a  series  of  experiments  on  frogs  wliich  Hoppe  '^  carried  out 
(1 858)  by  applying  one-fourtli  of  a  grain  of  caffein  to  the  muscles  of 
the  back,  he  concluded  that  caffein  causes  paralysis  of  the  nerves, 


HISTORICAL  REVIEW.  11 

spinal  cord,  and  brain,  sensation  being  paralyzed  before  movement. 
The  injurious  action  of  caffein  proceeds,  according  to  Hoppo,  from 
the  spinal  cord.  This  was  based  on  experiments  on  two  frogs,  Rana 
esculevta,  in  which  the  right  h'g  was  am])utat(Ml,  the  nerve  being  left 
intact,  while  the  nerve  of  the  other  leg  was  hgated.  At  the  end  of 
30  minutes  paralysis  was  more  marked  on  the  right  than  on  the  left 
side.  In  anotlicr  frog  of  the  same  species  he  resected  the  femoral 
nerva  on  the  right  side;  about  1^  hours  after  the  administration  of 
cafTcin  convulsions  were  observed.  The  left  leg  was  rigid,  but  the 
right  was  relaxed. 

Voit  ^'  (1860)  ligated  the  vessels  of  the  right  lower  extremity,  cut 
the  nerves  of  the  left  leg,  and  introduced  a  few  drops  of  cafTein 
solution  into  the  stomach.  Shortly  afterwards  tetanus  of  the  rig] it 
leg  occurred  on  toucldng  the  back  of  the  animal;  the  left  leg  was 
motionless.  Later  the  entire  body  exliibited  tetanic  convulsions. 
From  this  and  similar  experiments  Voit  concluded  that  cafFein  acts 
first  and  principally  on  the  central  nervous  sj^stem,  and  that  cafFein 
is  also  poisonous  to  nerve  and  muscle  fibers,  as  they  die  when  a  solution 
of  caffein  is  applied  to  them.  The  action  of  caffein,  according  to 
Voit,  is  similar  in  great  part  to  that  of  strychnin.  The  effect  on  the 
blood  vessels  is  particularly  interesting,  as  Voit  observed  dilatation 
of  the  vessels,  due  as  he  thought  to  muscular  paralysis,  and  also  trans- 
udation and  congestion  of  the  capillaries. 

Kurzak  ^^  (1860)  made  a  study  of  the  comparative  toxicity  of 
caffein  in  frogs  and  rabbits  and  came  to  the  conclusion  tliat  the  lethal 
dose  for  frogs  is  about  one-seventh  of  that  for  rabbits.  Caffein 
citrate  in  the  form  of  crystals  was  administered  in  both  cases  by 
mouth.  The  doses  given  to  frogs  were  1  to  1..5  grains.  lie  observed 
convulsions  and  increased  respiratory  activity  at  first;  after  one  hour 
respiration  diminislied  and  voluntary  muscular  activity  disappeared. 
Even  on  the  second  day  convulsions  were  sometimes  noticed.  Death 
occurred  at  the  end  of  the  first  or  second  day.  Experiments  on 
only  two  rabbits  were  reported,  0.8  gram  of  cafFein  citrate  causing 
the  death  of  one  at  the  end  of  13  hours.  The  symptoms  noticed  were 
the  same  practically  as  in  frogs,  but  it  is  interesting  to  observe  that 
ecchymosis  of  the  mucous  membranes  of  the  stomach  near  the  cardia 
was  the  only  lesion  found  on  autopsy.  Several  experiments  made 
on  different  days  on  the  other  rabbit  inchoated  that  the  toxic 
dose  exceeded  0.5  gram,  while  smaller  doses  caused  but  very  mild 
symptoms. 

According  to  Gentilhomme  "  (1867),  after  cafFein  the  reflexes  are  at 
first  diminished  and  then  disappear  altogether.  Death  is  produced 
by  stiffness  and  immobility  of  all  the  muscles,  particularly  of  the 
muscles  of  respiration,  thus  causing  asphyxia.  He  furthermore  held 
that  caffein  has  no  effect  on  cardiac  or  smooth  muscle  fiber,  its  action 


12  THE   TOXICITY   OF   CAFFEIN. 

being  specific  on  voluntary  muscle  fiber,  contractions  of  which  he 
observed  under  the  microscope,  thus  differing  completely  from  strych- 
nin, which  is  a  nerve  poison. 

These  observations  seemed  to  be  confirmed  by  Pratt  '•*  (1868),  who 
reported  that  the  isolated  posterior  extremities  and  muscle  fibers  of 
the  toad  placed  in  a  solution  of  caffein  (1  grain  to  a  wineglassful  of 
water)  for  three  minutes  were  contracted,  while  controls  placed  in 
distilled  water  were  relaxed.  This  experiment  is,  of  course,  defective, 
as  normal  salt  solution  should  have  been  used  in  both  cases.  ^'\nien 
the  muscular  fibers  previously  immersed  in  caffein  solution  were 
placed  under  the  microscope  violent  contractions  were  observed. 
The  same  author  administered  from  2  to  18  grains  at  a  dose  to  five 
healthy  young  men.  After  the  administration  of  12  grains  he  noticed 
mental  anguish,  tremors  of  the  hands  and  arms,  and  insomnia. 
Doses  under  5  grains  had  no  marked  effect  except  a  diminution  in  the 
frequency  of  the  pulse  and  wakefulness. 

About  the  same  time  Amory  *  (1868)  published  the  results  of  his 
Studies  on  the  toxicity  of  caffein  in  cats,  dogs,  rabbits,  and  pigeons. 
In  all  cases  very  large  doses  were  introduced  directly  into  the  stomach 
by  means  of  a  temporary  gastric  fistula.  Ten  grains  given  in  meat 
to  a  dog  caused  restlessness,  but  no  other  symptoms.  Doses  of  30 
grains  and  above  were  invariably  fatal.  Seventy-three  grains  given 
to  a  cat  caused  death  within  20  minutes. 

From  observations  on  frogs,  guinea  pigs,  rabbits,  and  on  one  dog, 
Leven  ^^  (1868)  concluded  that  caffein  which  he  gave  in  the  form  of 
the  citrate  in  doses  of  10  mg  to  frogs,  from  150  to  200  mg  to  guinea 
pigs,  and  three  to  four  times  the  latter  amount  to  rabbits,  stimulates 
the  central  nervous  system  and  the  voluntary,  cardiac,  and  smooth 
muscles.  He  found  that  0.9  gram  caffein  was  fatal  for  a  rabbit  when 
injected  subcutaneously,  while  1  gram  of  the  citrate  was  not  toxic 
for  a  dog  of  medium  size.  Caffein  applied  directly  to  muscle  fiber 
causes  tetanus  and  destroys  muscular  contractility,  while  a  nerve 
fiber  similarly  treated  loses  its  irritability. 

According  to  Johansen  *■*  (1869),  caffein  acts  directly  on  the  mus- 
cular fiber.  After  the  subcutaneous  injection  of  0.02  gram  of  caft'ein 
into  frogs,  he  observed  contraction  of  the  muscles  at  the  site  of  injec- 
tion, then  contraction  of  the  anterior  extremities,  and  finally  the 
posterior  extremities  become  rigid  and  extended.  Johansen  obsei-ved 
muscular  rigidity  after  caffein,  even  after  curara  was  injected,  or  after 
ligating  the  vessels,  or  cutting  the  nerves  which  supply  the  muscles. 
He  also  observed  that  large  doses  of  caffein  diminish  muscular  irrita- 
bility. When  cardiac  muscle  was  poisoned  with  caffein,  microscopical 
examination  showed  that  the  striations  disappeared.  Johansen  also 
states  that  reflexes  disappear  after  caffein  poisoning.  He  never 
observed  tetanus  in  frogs,  but  reported  tonic  and  clonic  convulsions  a.s 


HISTORICAL  REVIEW.  13 

a  result  of  cafTeiii  poisoning  in  mammals.  Somewhat  dilTercnt  cd'ccts 
of  caffein  in  frogs  were  obsei-ved  by  Buclihcim  and  Eisenmengor  ^* 
(1870).  After  the  injection  of  2  per  cent  of  the  citrate  the  frogs  soon 
become  inactive.  lie  also  observed  muscular  twitching  of  the 
extremities,  which  gradually  increased,  with  rigidity  of  the  muscles 
and  opisthotonos,  while  respiration  became  slow  and  superficial, 
finally  stopping  altogether. 

Aubert "  (1872)  studied  the  toxicity  of  caffein  in  man  and  other 
animals.  After  the  ingestion  of  0.36  gram,  he  obsei-vcd  dizziness, 
but  doses  of  0.12  and  0.24  gram  were  without  any  apparent  effect. 
On  the  other  hand,  a  dose  of  0.5  gram  of  caffein  was  followed  by 
increased  frequency  of  the  pulse,  which  soon  disappeared.  After  one 
hour  he  noticed  dizziness  and  trembling  of  the  hands,  which  likewise 
passed  away  soon.  The  injection  of  0.16  gram  of  a  2  per  cent  solution 
of  cad'ein  into  the  jugular  vein  of  a  rabbit  weighing  1,090  grams 
caused  tetanus  and  death  in  two  and  one-half  minutes,  and  0.12  gram 
injected  into  a  rabbit  weighing  980  grams  caused  death  in  one  minute. 
Much  larger  doses  could  be  borne,  however,  when  artificial  respiration 
was  resorted  to.  A  dog  which  was  given  3  grams  of  caflein  survived 
when  artificial  respiration  was  performed.  Aubert  reports,  on  the 
other  hand,  a  similar  experiment  with  0.25  gram  of  caffein  which 
terminated  fatally. 

That  caffein  may  give  rise  to  different  effects  in  various  species  of 
animals  was  observed  for  the  first  time  by  Bennett."  lie  studied  its 
action  on  frogs,  mice,  rabbits,  and  cats,  and  attempted  to  determine 
the  minimum  fatal  dose  in  rabbits  and  cats.  He  also  reported  experi- 
ments with  tliein.  In  his  first  communication  on  the  subject  he 
states  that  the  administration  of  thein  to  rabbits  first  increased  and 
then  diminished  the  frequency  of  respiration,  while  the  pulse  was 
decreased  in  frequency.  Caffein,  which  he  apparently  thought  was 
different  from  thein,  caused  increased  frequency  of  respiration,  while 
the  pulse  was  markedly  retarded  after  a  preliminary  acceleration. 
He  also  noticed  congestion  of  the  ears,  muscular  incoordination, 
tetanus,  paralysis,  diminished  reflexes,  and  contraction  of  the  pupils. 
Bennett  reported  the  minimum  fatal  dose  of  caffein  for  a  rabbit  weigh- 
ing 3.25  pounds  as  being  5.25-5.5  grains.  The  symptoms  in  cats 
after  the  administration  of  toxic  doses  of  thein  or  of  caffein  were 
groat  excitement,  paralysis  alternating  with  convulsions,  and  profuse 
salivation.  The  mmimum  fatal  dose  for  a  cat  weighing  5  pounds 
was,  accordmg  to  Bennett,  6  grains  of  caffein  and  5.5  grains  of  theia* 
Only  one  experiment  on  a  mouse  is  reported;  the  administration  of 
0.1  grain  proved  fatal.  The  symptoms  were  the  same  as  those 
observed  in  cats  and  rab])its  after  the  admmistration  of  caffein.  The 
experiments  on  frogs  indicate  that  the  symptoms  were  about  the 
same  as  those  previously  described  in  the  case  of  warm-blooded  ani- 


14  THE   TOXICITY   OP   CAFFEIN. 

mals  except  that  the  reflexes  are  almost  completely  lost  after  the  sub- 
cutaneous injection  of  doses  of  one-sixteenth  to  one- twelfth  of  a  grain. 
The  latter  dose  was  fatal  for  frogs.  It  would  be  of  interest  to  know 
the  comparative  toxicity  of  caffein  to  frogs  and  mammals,  but  unfor- 
tunately the  weights  were  not  reported. 

Schmiedeberg  '^  (1874)  noticed  that  the  administration  of  20  mg  of 
caffein  to  frogs  weighing  about  45  grams  was  followed,  in  Rana  escu- 
lenta,  in  about  25  minutes,  by  increased  reflexes,  7  minutes  later 
by  tetanus.  Several  attacks  occurred,  but  tonic  spasms  were  never 
observed.  On  the  contrary,  when  the  same  amount  of  caffein  was 
given  to  Rana  temporaria  weighing  45  grams  he  noticed  a  marked 
diminution  of  the  reflexes  and  tonic  rigidity  of  the  muscles  after  23 
minutes ;  the  reflexes  were  greatly  increased,  however,  about  24  hours 
later.  The  frogs  were  under  observation  for  three  days,  and  although 
symptoms  were  still  present  at  the  end  of  this  time  in  the  subjects  of 
both  species  tetanus  was  never  observed  in  Rana  temporaria. 

Peretti's  '"^  (1875)  studies  on  the  effects  of  caffein  were  confined 
chiefly  to  observations  on  dogs.  He  also  made  observations  on  a 
few  rabbits  and  reported  an  experiment  on  one  cat  to  which  he  admin- 
istered, by  subcutaneous  injection,  0.18  gram  of  caffein  per  kilo  and' 
noticed  increased  frequency  in  lachrymation  and  crying.  The  cat 
was  found  dead  the  next  day.  The  subcutaneous  injection  of  a  rabbit 
in  which  artificial  respiration  was  instituted  with  0.36  gram  of  caffein 
per  kilo  proved  fatal  soon  after  the  injection  without  any  manifesta- 
tion of  symptoms.  Small  doses  of  caffein,  0.1  gram,  given  to  a  rabbit 
weighing  3,670  grams,  failed  to  produce  any  visible  effects.  Doses 
under  0.1  gram  per  Idlo  Hkewise  failed  to  induce  any  symptoms  in 
dogs.  When  0.1  gram  of  caffein  per  kilo  was  given  by  mouth  or  sub- 
cutaneously  it  was  followed  by  restlessness,  salivation,  rigidity  of 
hind  legs,  and  vomiting.  In  both  instances  the  dogs  recovered.  The 
symptoms  were  more  severe  when  the  dose  was  increased  to  0.185 
gram  per  kilo,  but  even  in  this  case  the  dog  recovered.  A  dose  of  0.2 
gram  per  kilo,  however,  proved  fatal. 

Henneguy  ^^  (1875)  experimented  on  three  frogs  to  which  he  gave 
0.01  gram  of  caffein  citrate  subcutaneously.  He  observed  mild  stim- 
ulation of  the  nervous  system  and  of  the  muscles,  as  well  as  increased 
cardiac  activity.  Later,  voluntary  movement  and  respiration  disap- 
peared and  sensations  diminished,  but  convulsions  of  the  extremities 
appeared.  Cardiac  activity  was  then  diminished,  the  heart  being 
finally  arrested  in  systole.  Since  the  motor  nerves  retained  their  irri- 
tability even  after  the  reflexes  disappeared,  he  concluded  that  the 
loss  of  motion  was  due  to  the  action  of  caffein  on  the  nerve  centers. 

Binz  "  (1878)  reported  experiments  on  dogs  and  also  made  some 
observations  on  man  with  caffein.  The  subcutaneous  injections  of 
0.2  gram  caffein  may  prove  fatal  to  dogs,  although  some  survive  such 


HISTORICAL  REVIEW.  15 

a  (lose.  TJio  toxic  dose  in  man  varies  from  0.5  to  1.5  grams.  Dis- 
turbance of  the  circiilation,  such  as  palpitation  of  the  heart  and  full- 
ness of  pulse,  restlessnass,  and  diarrhea  were  the  symptoms  he 
observed. 

Extensive  investi^rations  on  the  action  of  caffein  were  carried  out 
by  Leblond^"  (1883),  who  studied  its  effect  on  the  circulation  in  man 
and  lower  animals,  and  its  toxicity  in  the  lower  animals  alone.  Five 
to  twenty  centigrams  of  caffein  and  0.06  to  0.25  gram  of  salicylate  of 
soda  were  dissolved  and  injected  into  the  muscles  of  the  thigh  of 
young  guinea  pigs  weighing  a  little  over  300  grams.  In  the  three 
experiments  reported  the  death  of  the  animals  occurred  after  23  min- 
utes, 40  minutes,  and  1  hour  and  20  minutes.  Symptoms  appeared 
in  from  10  to  15  minutes  after  the  injection  of  caffein.  Incoordination 
of  movements,  convulsions,  both  tonic  and  clonic,  opisthotonos, 
tremors,  increased  frequency  of  respiration,  ataxia,  paralysis  were 
the  symptoms  observed.  It  is  worthy  of  note  that  the  appearance 
of  paresis  preceded  the  convulsions.  Diminished  sensation  was 
reported  in  one  pig,  but  no  sensory  disturbances  nor  reflexes  had  been 
observed  in  the  other.  Two  rabbits,  one  of  wliich  received  0.5  and 
the  other  about  0.3  gram  of  caffein  per  kilo  with  equal  parts  of  sali- 
cylate of  soda,  were  injected  subcutaneously  into  the  thigh.  Dimin- 
ished sensation,  paresis  of  the  posterior  extremities,  hyperexeita- 
bUity,  convulsions,  opisthotonos,  dilation  of  the  veins  of  the  ear  were 
observed.  Death  followed  in  1  hour  and  23  minutes  in  one  rabbit 
and  in  3  hours  and  7  minutes  in  the  other. 

Filehne  "  (1886)  experimented  with  caffein  on  Rana  esculenta  and 
Bana  temporaria.  The  subcutaneous  injection  of  7  mg  of  caffein  into 
Rana  esculenta  caused  tetanus,  while  50  mg  given  by  mouth  caused 
tonic  spasms.  He  further  stated  that  the  difference  between  Rana 
esculenta  and  Rana  temporaria  as  regards  the  reaction  to  caffein  was 
one  of  degree  only. 

Amat  ^  (1889)  reported  experiments  on  three  guinea  pigs,  in  which 
0.4  to  0.5  gram  per  kilo  injected  subcutaneous!}^  proved  fatal  ^vithin 
38  and  44  minutes.  One  guinea  pig  which  received  0.1  gram  of 
caffein  per  kilo  survived.  The  symptoms  observed  in  the  two  fatal 
cases  were  gcnei-al  muscular  rigidity  and  convulsions. 

Parisot  ^^  (1890)  made  a  study  of  the  toxicity  of  caffein  on  different 
species  of  animals.  Unlike  most  of  his  predecessors,  however,  he 
reported,  at  least  in  some  cases,  the  weight  of  the  animals  on  which  he 
worked.  iVfter  the  subcutaneous  and  intramuscular  injections  of 
from  5  to  20  mg  of  caffein  into  Ranu  temporaria  weighing  from  14  to  16 
grams,  he  noticed  increased  irritability  at  first;  later,  a  loss  of  reflexes, 
inabihty  to  use  the  nmscles,  complete  muscular  rigidity  resembhng 
rigor  mortis,  and  also  cessation  of  heart  action.  The  effect  of  caffein 
})roduced  in  the  green  frog  was    analogous    to    that    observed  in 


16  THE   TOXICITY   OF    CAFFEIN. 

strychnin  poisoning.  Parisot  found,  however,  that  muscular  rigidity 
developed,  although  very  gradually,  also  in  the  green  frog,  but  it  set 
in  much  later  than  in  frogs  of  the  other  species  and  without  super- 
seding -the  clonic  convulsions.  According  to  Parisot,  the  muscular 
rigidity  after  cafl'ein  persists  after  the  destruction  of  the  brain  and 
spinal  cord,  thus  showing  that  it  is  not  of  nervous  origin.  He  further 
emphasized  the  difference  in  the  behavior  of  these  two  species  of  frogs 
toward  caffein  by  stating  that  he  never  observed  tetanic  convulsions 
in  the  red  frog.  His  experiments  also  indicate  that  the  green  frog  is 
more  resistant  to  caffein  than  Rana  temp'oraria,  as  the  same  doses 
which  are  fatal  for  the  latter  were  only  toxic  for  Rana  esculenta. 
The  number  of  experiments,  however,  is  too  few  to  justify  a  positive 
conclusion  on  this  point.  Parisot  also  made  some  experiments  on 
turtles.  The  results  he  obtained  show  that  caffein  is  at  least  as  toxic 
for  these  animals  as  for  the  frogs  he  experimented  upon,  0.33  gram 
per  kilo  (carapace  not  included  in  weight)  having  proved  fatal  within 
24  hours.  Two  experiments  on  one  pigeon  were  also  reported  by  the 
same  observer;  two  doses  of  0.06  gram  per  kilo  given  at  an  interval 
of  four  hours  caused  mental  depression  and  muscular  rigidity,  but  the 
pigeon  survived. 

Experiments  with  caffein  on  the  human  subject  made  by  Parisot 
showed  that  man  is  far  more  susceptible  to  this  substance  than  the 
other  animals  he  investigated.  After  the  ingestion  of  0.3  gram  of 
caffein  symptoms  of  intoxication  pointing  to  cerebral  disturbance 
appeared,  which  became  more  marked  when  the  size  of  the  doses  was 
increased. 

It  will  be  noticed  that  the  nature  of  the  action  of  caffein,  whether  it 
is  a  nerve  or  a  muscle  poison,  formed  the  subject  of  several  investiga- 
tions. Binz  "  (1890)  brought  forward  additional  evidence  in  support 
of  the  view  that  caffein  acts  primarily  on  the  ganglion  cells,  and  not  on 
the  muscle  directly.  This  he  has  shown  by  injecting  0.5  gram  into 
each  of  two  rabbits  after  cutting  the  sciatic  nerve  on  one  side ;  in  one 
case  he  also  resected  the  obdurator  and  crural  nerves  on  the  same  side. 
Clonic  spasms  developed  in  both  subjects  soon  after  caffein  was  given, 
but  in  each  rabbit  the  side  operated  upon  remained  paralyzed. 
Baldi  ^  (1891)  studied  the  action  of  caffein  on  Rana  esculenta.  After 
injecting  from  4  to  20  mg  tetanus,  such  as  observed  in  strychnin 
pois(ming,  was  noticed.  Frohner  ^^  (1892)  made  observations  on  the 
comparative  toxicity  of  caffein  in  domesticated  animals.  After  the 
administration  of  5  grams  of  caffein  sodium  salicylate  by  mouth  to  a 
dog  weighing  10  kilos,  he  noticed  salivation,  restlessness,  vomiting, 
and  convulsions  as  in  strychnin  poisoning.  Death  occurred  three 
hours  after  the  drug  wasgiven.  On  autopsyhe  noticed  mild  inflamma- 
tion of  the  mucous  membranes  of  the  stomach  and  intestines  and 
edema  of  the  lungs;  the  heart  was  in  diastole.     A  dose  of  2  grams  of 


HISTORICAL  REVIEW.  17 

cafTein  sodium  salicylate  given  to  the  same  animal  subcutaneously  two 
days  previously  provoked  only  very  slight  symptoms.  The  sub- 
cutaneous injection  of  10  grams  of  the  same  preparation  into  a  pig 
weighing  30  kilos  caused  death  in  two  and  a  half  hours,  with  the  pro- 
duction of  symptoms  of  disturbance  of  the  nervous  system  and  of 
gastrointestinal  irritation.  The  same  dose  per  kilo  of  body  weight 
given  to  a  goat  likewise  caused  death  in  two  and  a  half  hours  after  its 
administration.  P^xammation  on  autopsy  revealed  inflammation  of 
the  gastrointestinal  tract.  Similar  lesions  were  found  in  a  horse 
killed  by  100  grams  of  calTein,  in  which  he  also  noticed  hemorrhage 
of  the  mucosa  in  the  fundus  of  the  stomach. 

Gourewitch  ^*  (1907)  conducted  experiments  with  caffein  on 
rabbits,  pigeons,  and  wliite  rats.  It  appears  from  his  protocol  that 
single  doses  of  about  0.2  to  0.25  gram  caffein  per  kilo  given  subcuta- 
neously proved  to  be  fatal.  He  states,  however,  that  the  resistance 
to  caffein  was  markedly  diminished,  when  its  administration  was 
repeated  daily,  for  much  smaller  amounts  sufficed  to  cause  death  in 
these  animals.  A  dose  of  120  mg  of  caffein  per  kilo  proved  fatal  after 
the  third  injection.  When  the  dose  was  increased  to  170  mg  per  kilo, 
the  animal  succumbed  to  the  effects  of  caffein  after  the  second  injec- 
tion. His  experiments  on  the  other  animals  do  not  indicate  the 
degree  of  resistance  to  caffein,  since  the  weights  for  some  were  n<H 
given  while  for  the  others  no  attempt  was  made  to  determine  the 
minimum  toxic  or  fatal  dose. 

Maurel  ^'^  (1907)  studied  the  influence  of  different  methods  of 
administration  on  the  toxicity  of  caffein  on  frogs  and  rabbits.  He 
determined  the  minimum  toxic  and  lethal  doses  of  caffein  hydro- 
bromid  which  he  employed  in  1  to  2  per  cent  solutions.  He  concluded 
from  his  experiments  that  the  toxicity  of  caffein  when  given  by 
mouth  is  twice  as  great  for  the  frog  as  for  the  rabbit. 

More  recently  Hale  •^'  carried  out  a  number  of  experiments  on  guinea 
])igs  in  which  he  determined  the  toxicity  of  caffein  given  in  the  form 
of  the  citrate  and  made  into  a  pill  with  mucilage  of  acacia  and  arrow- 
root starch.  After  the  pill  was  dried  it  was  fed  to  the  animal,  due 
precaution  being  taken  that  none  of  it  was  lost  during  feeding. 
From  experiments  on  guinea  pigs  which  received  doses  of  ().;?  to  0.6 
gram  caffein  citrate,  the  following  data  have  been  reported:  Tliree 
decigrams  per  kilo  given  to  one  pig  was  not  fatal.  Of  three  pigs 
which  received  0.4  per  kilo,  one  died  and  two  survived.  Exactly 
the  same  results  were  obtained  in  three  others  which  received  0.5  per 
kilo.  Two  guinea  pigs,  which  received  0.55  and  0.6  per  kilo  each, 
died  after  15  and  7  hours,  respectively,  while  another  animal  survived 
a  dose  of  0.45  per  kilo. 

18594°— Bull.  14&— 12 2 


18  THE   TOXICITY   OF    CAFFEIN. 

This  review  of  the  Hterature  on  the  toxicity  of  caffein,  although 
bearing  evidence  of  considerable  investigation  and  extending  over 
three-quarters  of  a  century,  i?  largely  qualitative  in  character.  It 
appears  from  the  experiments  that  the  main  object  of  the  investiga- 
tions was  to  ascertain  the  nature  of  the  action  of  caffein,  whether  it 
is  a  muscle  or  a  nerve  poison.  The  comparative  toxicity  in  different 
species  of  animals  by  the  accurate  determination  of  the  toxic  and 
fatal  doses  received  but  little  attention.  To  fill  the  gap  in  our 
knowledge  of  the  toxic  effects  of  caffein,  the  present  investigation 
was  undertaken.  This,  it  will  be  seen,  proved  to  be  a  most  laborious 
task,  because  in  the  large  number  of  experiments  careful  observations 
showed  that  individuals  of  the  same  species  varied  considerably  in 
their  reaction  to  the  drug.  Numerous  other  factors,  as  will  be  shown, 
were  also  found  to  play  an  important  part  in  the  determination  of  the 
toxicity  of  caffein. 

ACUTE  CAFFEIN  INTOXICATION. 

The  object  of  these  experiments  was  to  determine  the  resistance 
to  caffein  in  various  species  of  animals  and  by  various  methods  of 
administration.  Caffein  was  therefore  given  by  mouth  and  injected 
subcutaneously  into  the  peritoneal  cavity,  into  the  muscles,  and  in- 
travenously. As  far  as  could  be  judged  by  appearance,  healthy  ani- 
mals were  selected  for  the  subjects  of  the  experiments,  but  as  it  is 
impossible  to  diagnose  with  any  degree  of  accuracy  the  condition  of 
the  animal  while  it  is  alive,  post  mortem  examinations  were  resorted 
to  in  many  cases  in  which  the  issue  of  the  experiment  was  fatal. 
Since  the  age  of  the  animal  may  modify  toxicity  full  grown,  as  well 
as  young,  animals  were  employed  for  these  experiments;  diet,  race, 
and  season  also  play  an  important  part  in  determining  the  toxicity 
of  a  drug  and  these  factors  were  also  taken  into  account  in  the  present 
investigation. 

EXPERIMENTS  ON  RABBITS. 

Animals  of  different  varieties  were  used  and  were  given  caffein  by  all  of  the  methods 
indicated  in  the  preceding  paragraph.  Some  of  the  rabbits  employed  in  these  experi- 
ments received  oats,  others  received  a  diet  exclusively  of  carrots  for  several  days  or  weeks 
previous  to  the  administration  of  caffein.  The  experiments  were  conducted  at  all  sea- 
sons of  the  year. 

SUBCUTANEOUS  INJECTION. 

From  a  study  of  the  literature  on  the  toxicity  of  caffein  it  seemed  that  about  150  mg 
per  kilo  is  probably  the  lethal  dose  for  the  rabbit  when  the  drug  is  injected  subcuta- 
neously. Preliminary  observations  were  therefore  carried  out  wilh  such  a  dose,  but 
it  was  found,  on  the  contrary,  that  this  amount  per  kilo  was  hardly  sufficient  to  induce 
symptoms  in  the  great  majority  of  cases. 


ACUTE   INTOXICATION — RABBITS.  19 

Series  A. 
(Doses  of  147  to  107  inK  of  cafloln  per  kilo  were  employod  in  these  experiments.] 

Rabbit  3S2.     Bclgicin  hare,  female.     Weight,  1,070  grains.     Diet,  oats. 

March  25:  8.5  cc  2  per  cent  caffein  (158  mg  per  kilo)  injected  subculaneously  at 
2.15  p.  m.;  4  p.  in.,  reflexes  increased;  5.45  p.  m.,  increases  of  reflexes  still  more 
marked . 

March  2(;:  Rabbit  looked  normal;  no  symptom.s  observed. 
Rabbit. 1^1.     Belgian  hare,  female.     Weight,  1,170  grams.     Diet,  oaLs. 

March  25:  2.15  p.  m.,  9  cc  2  per  rout  caffein  (153  mg  per  kilo)  injected  subcutane- 
ously;  4  p.  m.,  reflexes  increa.sed;  5.45  p.  ni.,  condition  the  same. 

March  2(j:  Rabbit  looks  normal;  no  symptoms  observed. 
Rabbit  3JS.     Belgian  hare,  female.     Weight,  1,300  grams.     Diet,  oats. 

March  25:  9  cc  2  percent  caffein  injected  subcutaneously  (1-50  mg  per  kilo);  4  p.  m., 
reflexes  increased;  5.45  p.  m.,  reflexes  increased  but  not  markedly. 

March  26:  No  symptoms;  rabbit  looks  normal. 
Rabbit  322.     White  female.     Weight,  1,065  grams.     Diet,  oats. 

March  17:  8  cc  2  per  cent  caffein  (150  mg  per  kilo)  injected  subculaneoiisly  at  11.55 
a.  m.;  12. .55  p.  m.,  reflexes  increased,  but  no  tetanus  nor  any  oilier  symptoms. 

March  18:  Rabbit  running  around  in  cage;  condition  apparently  normal. 

March  25:  Condition  of  rabbit  good. 
Rabbit  217.     White.     Weight,  1,355  grams.    Diet,  oats. 

October  29:  10  cc  2  per  cent  caffein  (147  mg  per  kilo)  injected  subcutaneously  at 
1.51  p.  m.    5.15  p.  m.,  rabbit  alive;  survived. 
Rabbit  219.     Maltese.     Weight,  1,S20  grams.    Diet,  oats. 

October  29:  14  cc  2  per  cent  caffein  injected  subcutaneously  at  1.40  p.  m.  (153  mg 
per  kilo);  5.15,  rabbit  alive;  survived. 
Rabbit  194.     White  female.     Weight,  1,490  grams.    Diet,  oats. 

October  14:  13  cc  2  per  cent  caffein  (174  mg  per  kilo)  injected  subcutaneously; 
increased  reflexes  and  tremors  were  observed. 

October  15:  Condition  of  rabbit  good;  no  symj^toms. 
Rabbit  191.     Brotvn  male.     Weight,  1,915  grains.     Diet,  oats. 

October  14:  16  cc  2  per  cent  caffein  (167  mg  per  kilo)  injected  subcutaneously; 
reflexes  increased  and  tremors  present. 

October  15:  Condition  of  rabbit  good. 

A  study  of  this  series  shows  that  about  150  mg  of  caffein  per  kilo  caused  increased 
reflexes  within  one  to  two  hours  after  injection.  ^Vhen  the  dose  was  increased,  as 
in  rabbits  194  and  191,  the  symptoms  were  more  pronounced;  150  mg  per  kilo  may 
be  regarded  as  the  minimum  dose  which  produces  symptoms  of  nervous  irritability 
Avhen  caffein  is  injected  subcutaneously.  Experiments  with  larger  doses  were  there- 
fore carried  out  in  order  to  determine  the  minimum  fatal  dose. 

Series  B. 

Approximately  0.2  gram  of  caffein  per  kilo  was  employed  in  these  experiments. 
Diet  and  raie  as  possible  factors  which  may  influence  the  toxicity  of  caffein  were 
made  the  subject  of  study  in  these  experiments  which  were  divided  into  two  groups 
as  shown  in  the  table,  page  25. 

Rabbit  95.    Gray  and  ivhite  male.     Weight,  1,478  grams.     Diet,  oats. 

February  27:  11.30  a.  m.,  15  cc  2  per  cent  caffein  (210  mg  per  kilo)  injected  sub- 
cutaneously; 2.20  p.  m.,  no  symptcms,  tremors  observed  when  handled,  but  not 
marked,  reflexes  slightly  increased,  no  muscular  rigidity  nor  any  other  symptoms; 
2.45  p.  m.,  rabbit  suddenly  became  very  restless,  jumped  off  the  table,  and  had 
convulsions;  3.45  p.  m.,  rabbit  died,  rigor  mortis  set  in  almost  immediately  after 
death. 

Rabbit  96.    Gray  and  white  male.     Weight,  1,585  grams.    Diet,  oats. 

February  27 :_  16  cc  2  per  cent  caffein  (200  mg  per  kilo)  injected  subcutaneously 
at  3.40  p.  m.;  increased  reflexes  observed  about  one  hour  after  caffein  was  injected, 
but  no  other  symptoms. 

February  28:  Rabbit  found  dead. 
Rabbit  112.     Bla/^h  female.     Weight,  875  grams.     Diet,  oats. 

March  18:  9  cc  2  per  cent  caffein  (205  mg  per  kilo)  injected  subcutaneously  at 
3  p.  m.;  3.30  p.  m.,  rabbit  became  restless,  reflexes  were  increased,  tremors  were 


20  THE   TOXICITY   OF   CAFFEIN. 

observed,  but  no  other  symptoms;  4.15  p.  m.,  rabbit  had  tremors,  was  handled  but 
this  failed  to  induce  tetanus,  10  minutes  later  tetanus  of  short  duration  with  recovery 
occuri'ed . 

March  19:  9  a.  m.,  found  dead. 
Rabbit  119.      Yellow  ivhite  female.     Weight,  1,060  grams.    Diet,  oats. 

April  17:  10  cc  2  per  cent  cafferu  (188  mg  per  kilo)  injected  subcutaneously  at 
2.10  p.  m. 

April  18:  Rabbit  found  dead. 
Rabbit  195.     White  female.     Weight,  1,309  grams.    Diet,  carrots,  since  October  7. 

October  14:  13  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  subcutaneously  at 
11.15  a.  m.;  2.25  p.  m.,  rabbit  had   convulsions  and  died.     Note:  Ulceration  of 
rectum  was  noticed. 
Rabbit  208.     Gray.     Weight,  1,068  grams.     Diet,  carrots,  October  7-15,  inclusive. 

October  15:  10  cc  2  per  cent  caffein  injected  subcutaneously  at  11  a.  m.;  1  p.  m., 
increased  reflexes  and  tremors  observed;  3.45  p.  m.,  tremors  were  marked  when 
rabbit  was  handled. 

October  16:  Rabbit  found  dead.     Note:  Looked  poorly  nourished. 
Rabbit  247.    Belgian  hare,  female.     Weight,  1,295  grams.    Diet,  oats  last  10  days  before 
expenment. 

November  10:  11  a.  m.,  urine  obtained  from  the  bladder  was  acid  to  litmus  and 
did  not  contain  sugar  or  albumen,  13  cc  2  per  cent  caffein  was  injected  subcutaneously; 
1.30  p.  m.,  15  cc  urine  obtained  was  markedly  alkaline  to  litmus  and  reduced  Feh- 
ling's  solution;  2.30  p.  m.,  reduction  of  urine  considerable,  marked  tremors  observed 
but  no  tetanus. 

November  11:  10.30  a.  m.,  95  cc  urine  collected  gave  moderate  reduction  of  Feh- 
ling's  solution,  no  symptoms,  condition  of  rabbit  seemed  to  be  good. 
Rabbit  248.     Belgian  hare,  female.     Weight,  1,305  grams.     Diet,  oats  the  last  10  days 
before  the  experiment. 

November  10:  11  a.  m.,  urine  markedly  acid  to  litmus,  no  albumen,  no  sugar; 
13  cc  2  per  cent  caffein  injected  subcutaneously;  1.30  p.  m.,  urine  was  slightly  alka- 
line to  litmus,  no  reduction  of  Fehling's  solution;  2  p.  m.,  reflexes  increased;  2.30 
p.  m.,  2  cc  urine  obtained  from  bladder,  sugar  abundant;  4.45  p.  m.,  reflexes  in- 
creased as  before,  but  no  tetanus. 

November  11:  10.30  a.  m.,  m'ine  collected  showed  slight  reduction  of  Fehling's 
solution;  otherwise  condition  of  rabbit  was  good;  rabbit  did  not  show  any  effects 
of  caffein. 

Rabbit  337.    Belgian  hare.     Weight,  1,040  grams.    Diet,  carrots,  March  31  to  April  6, 
inclusive. 

April  6:  3  p.  m.,  11  cc  2  per  cent  caffein  injected  subcutaneously  in  the  back 
(0.211  per  kilo);  4.30  p.  m.,  reflexes  much  exaggerated. 

April  7:  8.15  a.  m.;  condition  good,  no  symptoms.  , 

Rabbit  336.    Belgian  hare.     Weight,  1,040  grams.    Diet,  carrots,  March  31  to  April  6, 
inclusive. 

April  6:  3  p.  m.,  11  cc  2  per  cent  caffein  injected  subcutaneously  into  tissues  of 
the  back. 

April  7:  8.15  a.  m.,  no  symptoms,  condition  good. 

Although  symptoms  appeared  in  rabbits  of  Group  I  (see  table,  page  25)  about  the 
same  time  after  the  administration  of  caffein  as  in  the  rabbits  of  the  preceding  series 
all  of  them  terminated  fatally  2 J  hours  to  24  hours  after  its  administration.  Two 
of  these  rabbits  (Nos.  195  and  208)  were  fed  carrots  for  several  days  before  the  injec- 
tion of  caffein,  the  others  were  fed  oats.  Since  symptoms  and  death  appeared  in 
these  two  rabbits  about  the  same  time  as  in  the  rest  of  this  group  it  may  be  concluded 
that  caffein  is  not  less  toxic  when  carrots  are  fed  than  when  oats  form  the  exclusive 
diet.  But  since  rabbit  No.  208  was  poorly  nourished  and  ulceration  of  the  rectum 
was  observed  in  No.  195  it  is  quite  possible  that  caffein  might  be  less  toxic  in 
normal  rabbits  on  this  diet.  This  was  tested  in  rabbits  Nos.  336  and  337,  both  of 
which  seemed  to  be  free  from  abnormality  and  were  well  nourished.  Since  these 
rabbits  survived  and  manifested  mild  symptoms  only  of  intoxication  it  would  eeem 
that  a  carrot  diet  decreases  the  toxicity  of  caffein. 

It  was  suggested,  however,  that  another  factor  might  be  the  cause  of  the  greater 
resistance  to  caffein  in  these  two  rabbits,  namely,  race.  This  was  tested  in  rabbits  247 
and  248,  both  Belgian  hares.     Since  the  toxicity  of  caffein  in  these  two  rabbits  was  the 


ACUTE   INTOXICATION — RABBITS.  21 

same  aa  in  Noa.  336  and  337,  diet  as  a  factor  in  acute  caffein  intoxication  may  be  diw- 
regarded.  The  greater  resistance  to  caffein  of  these  four  rabbits  is  in  all  ])robability 
due,  therefore,  to  a  difference  of  race.  This  suggestion  gained  additional  support 
from  the  experiments  of  the  next  series. 

Series  C. 

The  object  of  these  experiments  was  to  determine  the  minimum  fatal  dose  for  the 
gray  rabbit  and  to  obtain  addit  ional  evidence  as  to  the  toxicity  of  caffein  in  the  several 
varieties  of  rabbits.  Eight  experiments  were  performed,  in  which  from  230  to  252  mg 
per  kilo  were  given.  The  white  rabbits,  three  in  number,  received  250,  242,  and  238 
mg  per  kilo.  All  the  others  (which  were  Belgian  hares)  received  from  236  to  252  mg 
per  kilo.  Two  of  the  white  rabbits  were  fed  carrots  for  one  week  preceding  the  injec- 
tion of  caffein.  The  other  was  fed  oats.  Three  of  the  Belgian  hares  were  on  a  diet 
of  oats,  two  were  fed  carrots  the  week  before  the  experiment  with  caffein. 

Rabbit  122.     While,  female.     Weight,  2,060  grams.    Diet,  oats. 

April  14:  25  cc  of  2  per  cent  caffein  (250  mg  per  kilo)  in  aqueous  solution  injected 
Bubcutaneously  in  the  back  at  1.35  p.  m.;  4.30  p.  m.,  tremors,  reflexes  increased, 
condition  otlierwise  good. 

April  lO:  9  a.  m.,  found  dead  in  cage.     Autopsy:  Liver  deeply  congested;  kidneys 
congested  in  cortex  and  medulla;  stomach  showed  small  hemorrhagic  areas,  perforating 
ulcers  in  pyloric  portion;  small  intestine  petechiated  on  mucosa;  lungs  and  spleen 
normal. 
Rabbit  234.     White,  female.     Weight,  1,650  gram^.    Diet,  November  2-9,  carrots. 

November  9:  10.45  a.  m.,  20  cc  2  per  cent  caffein  (242  mg  per  kilo)  administered 
subcutaneously. 

November  10:  9  p.  m.,  found  dead. 

Rabbit  335.    Gray  hare,  female.     Weight,  1,170  grams.    Diet,   March  31  to  April  7, 
carrots.  f 

April  7:  9.30  a.  m.,  14  cc  2  per  cent  caffein  solution  (240  m^  per  kilo)  injected  sub- 
cutaneously in  the  back;  10.30,  reflexes  much  increased,  rabbit  is  extremely  sensitive. 

April  8:  9  a.  m.,  found  dead.     Autopsy:  Liver  was  congested  and  contained  several 
coccidiosis  nodules;  stomach  distended  with  rather  dry  food  mass;  mucosa  exhibited 
mild  catarrhal  inflammation;  mucosa  of  intestines  also  slightly  inflamed. 
Rabbit  249.     Belgian  hare,  female.     Weight,  1,185  grams.    Diet,  oats. 

November  11:  Urine,  5  cc,  from  bladder  acid  to  litmus,  no  sugar,  no  albumin;  11.50 
a.  m.,  14  cc  2  per  cent  caffein  (236  mg  per  kilo)  administered  subcutaneously;  3.45 
p.  m.,  reflexes  increased,  hyperaeathesia  marked,  but  no  tetanus,  even  when  handled; 
30  cc  urine  collected  at  4  p.  m.,  reduction  of  Fehling's  solution  considerable. 

November  12:  10  a.  m.,  8  cc  urine  collected,  reduction  heavy,  only  a  few  cubic 
centimeters  obtained  from  bladder,  did  not  contain  any  sugar,  general  condition  of 
rabbit  good,  no  symptom  of  caffein  intoxication. 
Rabbit  321.     Yellow,  female.     Weight,  1,135  grams.    Diet,  oats. 

March  16,  1910:  11.50  a.  m.,  14  cc  2  per  cent  caffein  (246  mg  per  kilo)  injected  sub- 
cutaneously in  the  back;  2  p.  m.,  reflexes  increased,  is  very  sensitive,  started  to  run 
when  put  on  floor,  no  handling  except  what  was  required  for  removal  and  return  to 
cage,  feces  soft. 

March  17:  9.30  a.  m.,  condition  good,  rabbit  put  on  floor,  gait  normal,  but  does  not 
care  to  walk. 

March  18:  9  a.  m.,  walks  around  when  put  on  floor,  appetite  good,  condition  seems 
to  be  normal. 

March  25:  11  a.  m.,  rabbit  still  alive,  condition  good. 
Rabbit  250.    Belgian  hare,  female.     Weight,  1,4S5  grams.    Diet,  oats  at  least  two  days 
before  the  experiment. 

November  11:  11  a.  m.,  urine  obtained  from  bladder  acid  to  litmus,  no  albumin, 
no  sugar;  11.10  a.  m.,  18 cc,  2  per  cent  caffein  (252  mg  per  kilo);  3.45  p.m.,  reflexes  and 
hyperaesthesia,  no  tetanus;  4  p.  m.,  60  cc  urine,  marked  reduction  of  Fehling's  solution. 

November  12:  10  a.  m.,  condition  of  rabbit  good,  no  symptoms  of  caffein  intoxication, 
80  cc  urine  collected,  sugar  considerable,  only  a  few  cubic  centimeters  of  urine  obtained 
from  bladder,  no  reduction  of  Fehling's  solution. 


22  THE   TOXICITY    OF    CAFFEIN. 

Rabbit  SS4-     Belgian  hare,  female.     Weight,  1,270  grams.     Diet,  carrots,   March  SI  to 
April  7. 

April  7:  9.30  a.  m.,  15  cc  2  per  cent  caffein  (240  mg  per  kilo)  injected  subcutane- 
ously  in  the  back;  10.30  a.  m.,  reflexes  much  increased,  rabbit  extremely  sensitive. 

April  8:9  a.  m.,  condition  good,  no  symptoms. 
Rabbit  233.     White,  male.     Weight,  1,675  grams.    Diet,  carrots,  November  2  to  9. 

November  9: 10.50  a.  m.,  20  cc  2  per  cent  caffein  (238  mg  per  kilo)  injected  subcuta- 
neously,  no  symptoms  observed  until  5  p.m.,  when  increased  reflexes  and  hypersesthe- 
sia  were  noticed,  but  no  tetanus. 

November  10:  9  a.  m.,  paralysis  of  posterior  extremities;  died  at  1  p.  m. 

Analysis  of  the  results  obtained  in  the  experiments  of  this  series  and  inspection  of 
Table  I,  page  25,  show  that  all  four  of  the  rabbits  which  survived  doses  of  236  to  252  mg 
of  caffein  per  kilo  were  Belgian  hares.  Of  the  four  which  died  one  only  was  a  Belgian 
hare.  The  other  three  were  white  rabbits.  Two  of  these  were  fed  oats;  the  other  two 
received  carrots  during  seven  days  preceding  the  administration  of  caffein.  This  diet 
does  not  seem  to  be  a  factor,  therefore,  in  the  toxicity  of  caffein.  Moreover,  it  may 
be  observed  that  rabbit  No.  122,  which  was  fed  oats,  died  after  receiAdng  250  mg  per 
kilo,  while  rabbit  No.  250  received  the  same  diet  and  survived  the  same  dose  of  caffein 
per  kilo. 

Experiments  234  and  334  offer  another  illustration  that  the  toxicity  of  caffein  is  not 
dependent  upon  diet,  since  both  rabbits  were  fed  carrots,  but  the  same  dose  of  caffein 
caused  only  symptoms  in  one  while  it  proved  fatal  to  the  other.  It  is  evident,  there- 
fore, that  the  difference  in  resistance  to  caffein  shown  in  these  experiments  is  in  all 
probability  due  to  race,  the  Belgian  hare  being  more  resistant  to  caffein  than  rabbits 
of  other  varieties.  Rabbit  No.  335  seems  to  be  an  exception,  but  the  post-mortem 
examination  showed  the  presence  of  coccidiosis  of  the  liver.  As  will  be  shown  later, 
wherever  this  condition  prevailed  even  smaller  doses  of  caffein  proved  fatal. 

Series  D. 

To  obtain  additional  evidence  regarding  the  resistance  of  the  various  races  of  rabbits 
to  caffein  and  to  ascertain  the  smallest  dose  which  is  surely  fatal  to  the  gray  rabbit  or 
Belgian  hare  was  the  object  of  this  series  of  experiments.  The  diet  in  all  cases  con- 
sisted of  oats,  which  was  given  ad  libitum  excepting  to  rabbit  No.  235,  which  received 
carrots  for  one  week  previous  to  the  injection  of  caffein.  The  doses  administered 
ranged  from  267  to  300  mg  per  kilo  and  were  administered  to  different  varieties  of  adult 
rabbits. 

Rabbit  253.    Brown  and  black,  male.     Weight,  1,600  grams.    Diet,  oats,  November  9  to  12. 

November  12:  11.30  a.  m.,  urine  from  bladder  acid,  no  albumen,  no  sugar;  11.35 
a.  m.,  22  cc  2  per  cent  caffein  (275  mg  per  kilo)  injected  subcutaneously;  11.45  a.  m., 
rabbit  jumped  off  the  table,  had  convulsions,  retraction  of  head  and  opisthotonos, 
general  tremors,  anterior  extremities  stretched  out,  posterior  extremities  almost 
normal,  frequent  twitchings;  died  at  12.15  p.  m. 
Rabbit  252.     Black,  female.     Weight,  1,335  grams.     Diet,  oats,  November  9  to  12. 

November  12:  11.30  a.  m.,  18  cc  2  per  cent  caffein  (270  mg  per  kilo)  injected 
subcutaneously.  Urine  obtained  from  bladder  before  injection,  acid,  no  albumen, 
no  sugar,  color  normal,  tremors  and  great  excitement  noticed  about  12  noon;  4.30 
p.  m.,  when  handled,  showed  unusual  restlessness  and  excitement  followed  by  con- 
vulsions with  opisthotonos;  occasional  twitching,  condition  bad.  Died  4.35  p.  m. 
Rabbit  327.     White,  female.     Weight,  820  grams.     Diet,  oats,  March  S  to  16. 

March  16:  11.45  a.  m.,  12  cc  2  per  cent  caffein  (292  mg  per  kilo)  injected  subcu- 
taneously in  the  back;  2  p.  m.,  found  dead,  but  was  still  warm.  Autopsy:  Hemor- 
rhagic area  at  point  of  injection  into  spinal  muscles;  subcutaneous  abdominal  region 
exhibited  a  large  area  of  cheesy  purulent  material;  liver  and  spleen  were  engorged; 
bladder  filled;  intestines  normal. 
Rabbit  340.     While  and  brown  male.     Weight,  1,465  gravis.     Diet,  oats. 

March  30:  3.20  p.  m.,  20  cc  of  2  per  cent  caffein  (273  mg  per  kilo)  injected  subcu- 
taneously in  back. 

March  31:  9  a.  m.,  found  dead. 


ACUTE   TNTOXICATlON — RABBITS.  23 

Rabbit  341.     White  and  brown.     Weight,  1,4W  grams.     Diet,  oats 

March  'M):  3.20  p.  m.,  20  cc  2  per  cent  caflein  (270  nii:  per  kilo)  injected  snbcu- 
tanoously  in  back;  4.40  p.  m.,  found  in  dyin^  condition,  had  convulsions;  4.45  p.  ni., 
dead. 
Rabbit  S'26.     White,  male.     Weight,  1,64.')  grams.     Diet,  oats,  March  8  to  16. 

March  IG,  1!)10:  12  noon,  20  cc  2  per  cent  caffein  (243  mg  per  kilo)  injected  aubcu 
taneously  in  the  back;  2  p.  m.,  tremors  marked,  hypersensitive,  started  to  run  when 
put  on  floor;  rabbit  was  not  handled  any  more  than  was  required  for  his  removal  from 
and  return  to  ca>:e. 

March  17:  !».30  a.  m.,  tremors  still  present  and  marked,  otherwise  general  condition 
good;  no  other  symptoms. 

March  IS:  9.30  a.  m.,  no  appetite,  tremors  still  present,  general  condition  poor; 
died  about  2  p.  m. 
Rabbit  '235.     Belgian  hare,  male.     Weight,  1,870  grains.     Diet,  carrots,  November  2  to  9. 

November  10:  11.05  a.  m.,  25  cc  2  per  cent  canein  (2G7  mg  per  kilo)  injected  subcu- 
taneously;  reflexes  increased  and  tremors,  but  no  tetanus  observed;  found  dead  next 
morning. 
Rabbit  316.     Belgian  hare,  female.     Weight,  860  grams.     Diet,  oats,  March  8  to  16. 

March  16,  1910:  11.40  a.  m.,  12  cc  2  per  cent  caffein  (267  mg  per  kilo)  injected  sub- 
cutaneously  in  the  back;  2.15  p.  m.,  reflexes  somewhat  increased,  but  not  markedly 
so;  walked  when  put  on  floor;  gait  clumsy  and  slow;  tremors  of  head  observed;  2.35 
p.  m.,  rabbit  l}"ing  in  his  cage,  posterior  extremities  extended  and  rigid,  anterior 
extremities  flexed,  head  retracted;  is  still  breathing;  occasional  spasms  observed. 
Kabbit  died  at  3  p.  m.  Autopsy:  No  lesion  at  point  of  injection  in  dorsal  spinal 
muscles;  liver  and  spleen  engorged;  intestines  injected;  other  organs  apparently 
normal. 
Rabbit  395.     Belgian  hare,  male.     Weight,  1,410  grams. 

August  18: 1  p.  m.,  20  cc  2  per  cent  caffein  (2S3  mg  per  kilo)  injected  subcutaneously 
in  the  back;  4  p.  m.,  reflexes  markedly  increased;  5  p.  m.,  reflexes  about  the  same, 
but  no  tetanus. 

August  19,  9.15  a.  m.:  Reflexes  increased  markedly. 

August  21,  weight,  1,215  grams.  Given  275  mg  per  kilo  of  caffein;  no  symptoms 
observed. 

August  23,  found  dead.     Autopsy:  Liver  greatly  engorged;  stomach  fairly  well  dis- 
tended and  mucous  membrane  in  a  slightly  inflammatory  condition;  contents  of 
small  intestine  li(juid  in  nature,  but  walla  of  same  appeared  normal;  other  organs 
nonnal  in  appearance. 
Rabbit  396.     Belgian  hare,  female.     Weight,  1.475  grams.     Diet,  oats. 

August  18:  1  p.  m.,  20  cc  2  per  cent  caffein  (272  mg  per  kilo)  injected  subcutaneously 
in  the  back;  4  p.  m.,  reflexes  increased  markedly;  5  p.  m.,  reflexes  increased  markedly 
but  no  tetanus. 

August  15:  10.30  a.  m.,  reflexes  still  increased  very  markedly;  rabbit  jumps  when 
touched. 

August  21:  Weight,  1,245  grams.  Injected  subcutaneously  275  mg  of  caffein  per 
kilo;  reflexes  increased,  posterior  extremities  stiff  over  hour  later. 

August  22:  9  a.  m..  found  dead.  Autopsy:  Thoracic  organs  normal  in  appearance; 
stomach  distended  and  mucous  membrane  affected  with  a  catarrhal  inflammation; 
contents  of  stomach  were  covered  with  a  shiny  mucus;  contents  of  small  intestine 
liquid  in  nature  and  bile  stained;  liver  showea  a  coccidial  infestation;  kidneys  and 
spleen  normal  in  appearance. 
Rabbit  397.    Belgian  hare,  male.     Weight,  1,375  grams.    Diet,  oats. 

August  19:  10.30  a.  m.,  20  cc  2  per  cent  caffein  (290  mg  per  kilo)  injected  subcu 
taneously  in  the  back. 

August  22:  9  a.    m.,    found   dead.     Autopsy:  Stomach   distended   with  ingesta; 
mucous  membrane  exhibited  a  catarrhal  inflammation  with  excessive  secretions; 
major  portion  of  intestines  showed  a  condition  similar  to  that  of  stomach,  contents 
consisting  mainly  of  a  shiny  mucus;  liver  enlarged;  other  organs  apparently  normal. 
Rabbit  398,  Belgian  hare,  female.     Weight,  1,570  grams.     Diet,  oats. 

August  19:  10. 30  a.  m. ,  23  cc  2  per  cent  caffein  (293  mg  per  kilo)  injected  subcutane- 
ously in  the  back;  4  p.  m.,  found  dead.     Autopsy:  Thoracic  organs  seemingly  normal; 
mucous  membrane  of  stomuch  exbibited  a  catarrhal  inflammation  generally;  large 
intestines  somewhat  impacted  but  walls  appeared  normal;  other  organs  normal. 
Rabbit  399,  Belgian  hare,  male.     Weight,  1,725  grams.     Diet,  oat^. 

August  19:  10.30  a.  m.,  26  cc  2  per  cent  caffein  (300  mg  per  kilo)  injected  subcutane- 
ously in  the  back;  found  dead  at  4.30  p.  m.     Autopsy:  Lungs  slightly  congested;  liver 


24  THE   TOXICITY   OF   CAFFEIN". 

engorged  and  friable;  gall  cyst  well  filled;  stomach  exhibited  catarrhal  gastritis;  injec- 
tion of  mesenteries  and  intestines;  kidney  showed  marked  cortical  congestion. 

The  results  of  the  experiments  of  this  series  likewise  indicate  that  the  Belgian 
hare  is  more  resistant  to  caffein  than  the  rabbits  of  other  varieties.  Thus,  of  the  four 
gray  rabbits  (Nos.  235,  316,  395,  and  396),  which  received  267  to  283  mg  of  caffein  per 
kilo,  two  died  and  two  lived, «  one  of  which,  396,  showed  the  presence  of  coccidiosis 
of  the  liver.  On  the  other  hand  it  will  be  observed  that  the  black  and  white  rabbits 
which  received  from  270  to  275  mg  of  caffein  per  kilo  all  died  from  the  effects  of  the 
drug;  one  within  1  hour  and  25  minutes  and  another  within  50  hours  after  the  admin- 
istration of  the  caffein,  while  Ko.  340  died  in  the  night.  Fiuthermore  it  will  be  noted 
that  of  the  last  three  rabbits  of  this  series,  which  were  Belgian  hares  and  received 
290,  293,  and  300  mg  of  caffein,  two  died  six  hours  after  the  injection,  while  the  other. 
No.  397,  lived  three  days.  The  minimum  fatal  dose  of  caffein  for  Belgian  hares  is, 
therefore,  about  290  to  300  mg  per  kilo  when  injected  subcutaneously,  which  is  about 
50  per  cent  greater  than  for  rabbits  of  other  varieties. 

Series  E. 

It  was  shown  in  series  A  that  0.15  caffein  per  kilo  caused  symptoms  of  intoxication. 
Before  concluding,  however,  that  this  is  the  smallest  dose  which  causes  symptoms  of 
poisoning,  a  number  of  experiments  were  performed  with  smaller  doses.  It  was 
found  that  in  the  great  majority  of  cases  0.1  caffein  per  kilo  may  cause  diiiresis, 
but  no  ners^ous  or  muscular  symptoms.  In  some  rabbits,  however,  even  such  a  dose 
proved  fatal.  Post-mortem  examinations  in  these  cases  showed  the  presence  of. 
coccidiosis  of  the  liver,  and  it  will  be  recalled  that  similar  observations  were  made 
before.  It  is  quite  possible,  therefore,  that  coccidiosis  of  the  liver  is  an  important 
factor  in  decreasing  the  resistance  to  caffein.  Experiment  551  (p.  25)  shows  that 
other  conditions  may  likewise  increase  the  toxicity  of  caffein. 

Rabbit  325.     White,  female.     Weight,  1,065  grams.    Diet,  oats. 

March  17:  11  a.  m.,  6  cc  2  per  cent  (112  mgper  kilo)  caffein  injected  subcutaneously 
in  the  back.     About  5  cc  of  urine  squeezed  out  from  bladder  before  injecting  caffein. 

March  17:  1  p.  m.,  hind  legs  crossed  and  stretched  out,  front  legs  also  extended; 
rabbit  lying  stretched  out  on  her  belly. 

March  17:  5.40  p.  m.,  rabbit  still  alive,  condition  somewhat  improved. 

March  18:  9  a.  m.,  found  dead,  stiff  and  cold.     Autopsy:  Hemorrhagic  area  at  point 
of  inoculation;  subcutaneous  region  of  both  thighs  presented  a  hemorrhagic  infiltra- 
tion of  the  tissues;  liver  contained  lesions  of  coccidiosis;  other  organs  apparently 
normal. 
Rabbit  330.     Belgian  hare,  female.     Weight,   933  grams;  poorly  nourished. 

March  18:  3.35  p.  m.,  5  cc  2  per  cent  caffein  (107  mg  per  kilo)  injected  into  subcu- 
taneous tissues  in  the  back;  5.30  p.  m.,  no  symptoms. 

March  19:  9  a.  m.,  no  symptoms. 

March  25:  Weight,  825  grams. 
Rabbit  329.     Belgian   hare,    male.     Weight,    775  grams;  poorly   nourished.     Received 
March  18. 

March  18:  3.30  p.  m.,  4  cc  2  per  cent  caffein  (103  mg  per  kilo)  injected  into  sub- 
cutaneous tissues  in  the  back;  5.30  p.  m.,  no  symptoms. 

March  19:  9  a.  m.,  no  symptoms. 

March  25:  Rabbit  alive  in  good  condition;  weight,  825  grams. 
Rabbit  320.     Black,  male.     Weight,  1,040  grams.     Diet,  oats. 

March  17:  11  a.  m.,  6  cc  2  per  cent  caffein  (115  mg  per  kilo)  injected  subcutaneously 
in  the  back;  only  a  few  drops  of  urine  oV^tained  from  bladder  before  injecting  caffein; 
1p.m.,  rabbit  very  restless;  ran  away  when  placed  on  floor;  cried  when  touched  with 
a  piece  of  paper;  no  tremors  observed,  but  rabbit  became  exhausted  and  was  unable 
to  walk;  legs  extended  out;  after  running  for  about  a  minute  dyspnoea  was  very 
marked,  but  rabbit  soon  raised  himself  on  his  legs;  5.40  p.  m.,  rabbit  up  on  his  legs. 

a  Survived  first  dose. 


ACUTE   INTOXICATION — RABBITS. 


25 


March  18:  9  a.  m.,  found  dead,  but  still  warm.     Autopsy:  Lungs  studded  with 
small  grayish  white  nodules,  adhesions  to  eoslal  pleura;  j)robably  lesions  of  coccidiosis; 
liver  studded  with  coccidiosis  nodules.     Hemorrhages  at  point  of  inoculation. 
Rabbit,  551.     Gray,  female.     Weight,  January  26, 1,650  grams.     Diet,  oats;  fed  20  cc  of 
25  per  cent  alcohol  daily  from  January  26-Sl. 

January  3i:  Weight,  1,450  grams;  10.20  a.  ra.,  temperature  101.0°;  10.45,  a.  m., 
temperature  101.6°;  received  7  cc  2  per  cent  caffein  subcutaneously  into  back;  11.15 
a.  m.,  convulsions  of  short  duration;  raised  himself  on  posterior  legs,  anterior  legs 
wide  apart;  4.10  p.  m.,  looked  normal,  not  hypersensitive;  4.30  p.  m.,  condition 
seemed  to  be  good. 

February  1:  9  a.  m.,  found  dead,  was  alive  at  5.30  p.  m.  of  previous  day.  Autopsy: 
Lesions  found  involved  thoracic  cavity  maiidy;  lungs  were  hepatizecl  and  a  fibre 
plastic  exudate  caused  them  to  adhere  to  costal  pleura;  liver  engorged  and  appeared 
fatty;  no  marked  lesions  affecting  digestive  tract,  a  slight  catarrh  of  stomach  being 
the  oTdy  noticeable  feature;  kidneys  and  spleen  normal. 

Table  1. — SuhctUaneous  injections  of  caffein — rabbits. 

SERIES  A. 


No. 

Weight. 

Caffein 
per 
kilo 

Appearance  of  symp- 
toms in— 

Duration  oflifc 

Diet. 

Remarks. 

332 

Grams. 
1,070 
1,170 
1,200 
1,065 
1,355 
1,820 
1,490 
1,915 

Mg. 

158 
153 
150 
150 
147 
153 
174 
167 

1  hour  45  minutes 

.    do 

Oals 

...do 

"%o. 

331 

do 

328 

do 

do 

...do 

Do. 

322 

do 

...do 

White. 

217 

do 

...do 

Do. 

219 

do 

...do 

Maltese. 

194 

do 

...do 

White. 

191 

do 

...do 

Light  brown. 

SERIES  B,  GROUP  I. 


95 

1,478 

210 

96 

1,585 

200 

112 

875 

205 

119 

1,060 

188 

195 

1,300 

200 

208 

1,068 

188 

2  hours  50  minutes. 

1  hour 

30  minutes 


2  hours. 


3  hours  10  minutes. 

About  18  hours 

do 

do 

3  hours  10  minutes. 
About  24  hours 


Oats 

..do 

...do 

..do 

Carrots  .. 
..do 


White. 
Gray  white. 
Black. 

Yellow  white. 
White. 
Gray. 


SERIES  B,  GROUP  II. 


''47 

1,295 
1..305 
1,040 
1.045 

200 
200 
211 
211 

2  5  hours ...        

Survived 

Oats 

...do 

Gray. 
Do. 

'MS 

3  hours 

do 

3'17 

1.5  hours 

do 

Carrots. . . 
...do 

Do. 

■<?6 

..do 

do 

Do. 

SERIES  C. 


122 

2,060 

250 

234 

1,650 

242 

335 

1,170 

240 

249 

1,185 

236 

321 

1,135 

246 

250 

1,435 

252 

334 

1,270 

240 

'233 

1,675 

238 

2  hours  55  minutes . . . 


Ihour 

4  hours 

2  hours  10  minutes. 
4  hours  35  minutes. 
1  hour 


238     6  hours  10  minutes . 


1.5  days 

About  24  hours. 

do 

Survived 

do 

do 

.do. 


26  hours do 


Oats 

Carrots... 

..do 

Oats 

..do 

..do 

Carrots. . . 


White. 

Do. 
Gray  coccidiosis. 
Gray. 
Yellow. 
Gray. 

Do. 
White. 


2G 


THE   TOXICITY   OF    GAFFEIlSr. 


Table  1. — Subcutaneous  injections  of  caffein — rabbits — Continued. 
SERIFS  D. 


Caffein 

No. 

Weight. 

per 
kilo. 

Grama. 

Mg. 

253 

1,600 

275 

252 

1,335 

270 

327 

820 

292 

340 

1.465 

273 

341 

1,450 

270 

32(5 

1,645 

243 

235 

1,875 

267 

31(5 

860 

267 

395 

1,410 

283 

395 

1,215 

275 

■Am 

1,475 

272 

396 

1,245 

275 

397 

1,375 

290 

39« 

1,570 

203 

399 

1, 725 

300 

Appearance  of  symp- 
toms in— 


Duration  of  life. 


Diet. 


Remarks. 


10  minutes. 
30  minutes. 


2  hours. 


2  hours  45  minutes. 

3  hours 

do 

do 

Ihour 


35  minutes 

4  hours  55  mmutes . 

2  hours  15  minutes. 

About  18  hours 

1  liour  25  minutes.. 

50  hours 

20  hours 

3  hours  20  minutes. 

Survived 

About  2  days 

Survived 

About  18  hours 

3  days 

5.5  hours 

6  hours 


Oats... 
...do... 
...do... 
...do... 
...do... 
...do... 
Carrots. 
Oats... 


Oats. 
..do. 
..do. 
..do. 
..do. 
..do. 


Brovs^n  and  black. 

Black. 

Wliite. 

White  and  brown. 

Do. 
White. 
Gray. 

1)0. 

Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 


SERIES  E. 


S-'o 

1,065 

935 

775 

1,040 

1,450 

112 
107 
103 
115 
100 

2  hours 

Less  than  22  hours 

Survived 

Oats 

White  female. 

330 

None 

Gray. 

T'9 

.do 

.do 

Gray  male. 
Black  male. 

r>{\ 

2  hours 

46  hours 

Oats 

...do 

I'll 

30  minutes 

Less  than  24  hours 

Gray  female. 

ADMINISTRATION  BY  MOUTH. 

These  experiments  were  carried  out  on  two  varieties  of  rabbits,  the  white  and  the 
gray.  The  diet  consisted  chiefly  of  oats,  but  in  a  few  cases  carrots  formed  the  exclusive 
diet.  Food  and  water  were  given  ad  libitum.  A  2  per  cent  solution  of  caffein  was 
administered  through  a  stomach  tube.  Since  the  resistance  to  most  drugs  is  com- 
monly supposed  to  be  greater  when  given  by  mouth  than  when  administered  by  any 
other  path,  doses  of  175  to  200  mg  per  kilo  were  fed  in  a  series  of  preliminary  experi- 
ments, all  of  which  were  performed  on  gray  rabbits  weighing  from  865  to  1,135  grams, 
and  which  were  fed  carrots  for  several  days  previous  to  the  experiment.  Three  of  the 
rabbits  survived,  two  mthout  showing  any  symptoms;  in  the  other  case  paralysis  of 
the  posterior  extremities  was  observed  five  hours  after  he  received  caffein  and  he  was 
found  dead  the  next  morning.  Unfortunately  no  autopsy  was  performed.  The  low 
resistance  to  caffein  of  this  animal  was  probably  due  to  some  abnormal  condition  which 
developed  about  the  time  of  the  experiment,  since  this  rabbit  received  325  mg  of 
caffein  per  kilo  two  weeks  previously  and  increased  reflexes  only  were  observed  as  a 
result  of  this  treatment.  Hence  200  mg  of  caffein  per  kilo  can  not  be  considered  the 
toxic  dose  when  fed  by  mouth.  In  the  following  experiments  larger  doses  were 
therefore  given. 

Series  A. 

Rabbit  24S.     Belgian  hare.     Weight,  1,170  grams.     Diet,  oats. 

November  17:  1.20  p.  m.,  19.5  cc  2  per  cent  caffein  (330  mg  per  kilo)  administered 
by  the  mouth;  4.30  p.  m.,  somewhat  hypersensitive. 

November  19:  No  symptoms;  at  9  a.  m.,  urine  collected,  no  reduction  of  Fehling's 
solution;  rabbit  survived . 

Rabbit  241.     White  male.     Weight,  1,-380  grams.     Diet,  oats. 

November  17:  1.15  p.  m.,  20  cc  2  per  cent  caffein  (290  mg  per  kilo)  administered 
by  the  mouth;  4.30  p.  m.,  some  hypersensitiveness,  but  no  other  symptoms. 

November  18:  9  a.  m.,  urine  collected,  no  reduction  of  Fehling's  solution;  no 
eymptoms;  rabbit  Burvived. 


ACUTE   INTOXICATION — RABBITS.  27 

liubbit  249.    Belgian  hare.     Weiffhl,  890  grams.     Diet,  oats. 

Noveinher  17:  I.IW  p.  in.,  14.5  rr  2  por  ctMit  futfein  (325  mg  per  kilo)  administered ; 
4.30  p.  Ml.,  hyporsouHitiveiiws;  110  oLluT  Hyiiiptom.s. 

November  18:  10  a.  in.,  no  Hymptdni.s;  nriiu'  collected,  no  reduction;  rabbit  sur- 
vived. 

Series  H. 

The  object  of  these  experiments  was  to  (let(!rmine  tlio  minimum  fatal  ditse  of  caffein 
in  the  two  varieties  of  rabbits,  the  white  ami  the  K'li.V-  AH  of  the  animals  selected 
were  api)roximately  of  the  same  weij^ht. 

liubbit  J.i9.     Belgian  hare,  male.      Weight,  9.>V5  grams.     Diet,  outs. 

November  lit:  1  p.  m.,  17  cc  2  j)er  cent  callVin  (3G3  mg  per  kilo)  adminiHlcrcil  ])y 
mouth,  followed  by  10  cc  of  0.9  j)er  cent  salt  solution. 

November  20:  Urine  examined,  no  sugar  found,  no  symptom  noticed  at  any  time 
after  injection. 
Rabbit '254.     Belgian  hare,  female.     Weight,  975  grams.     Diet,  oats. 

November  1!):  4.05  p.  m.,  18  cc  2  per  cent  callein  (3(ji)  mg  per  kilo)  administered  by 
mouth,  followed  by  10  cc  of  0.9  per  cent  salt  solution. 

November  20:  9  a.  m.,  rabbit  found  dead. 
Rabbit  267.    White.     Weight,  1,050  grams.     Diet,  oats. 

November  23:  12.10  p.  m.,  IS  cc  2  per  cent  caffein  (342  mg  per  kilo)  given  by  mouth, 
followed  by  ISccsalt  solution;  1  p.  m.,  increased  reflexes,  tremors  marked  but  no  teta- 
nus; 1.0")]).  m.,  rabbit  stretched  on  abdomen,  posterior  exlremiti(!H  in  extended  position 
and  paralyzi'd,  soon  after  clonic  spasms  set  in,  which  recurred  about  every  minute; 
1.1  I  p.  m.,  tetanus  and  death.  Aulopsij:  Liver  showed  fatty  degeneration;  slight  in- 
flammation of  stomach  and  intestines;  other  organs  normal. 
Rabbit  268.     White.     Weight  1,1  UO  grams.     Diet,  outs. 

November  23:  20  cc  2  per  cent  caffein  (3G3  mg  per  kilo)  administered  by  mouth,  fol- 
lowed by  20  cc  salt  solution;  1.15  p.  m.,  somewhat  hypensensitive;  4.30  p.  m.,  tremors 
fairly  marked,  no  urine  ])assed,  about  2  cc  of  bloody  looking  urine  obtained  from  blad- 
der, which  contained  albumen  and  a  considerable  amount  of  glycogen;  rabbit  died. 
Rabbit  419,  Belgian  hare,  male.      Weight,  1,600  grams.     Diet,  oats. 

September  2(5:  10  a.  m.,  28  cc  2  per  cent  caffein  (350  mg  per  kilo)  given  by  mouth; 
reflexes  increased  at  4  ]).  m.;  6  p.  m.,  reflexes  still  increased,  no  other  symptoms. 

September  27:  9  a.  m.,  found  dead.     Autopsy:  Lungs,  liver,  and  kidneys  congested; 
other  organs  normal. 
Rabbit  420.    Belgian  hare,  male.     Weight,  1,250  grams.     Diet,  oats. 

September  2(i:  10  a.  m.,  22  cc  2  per  cent  caffein  (352  mg  per  kilo)  given  by  mouth; 
11.35  a.  m.,  convulsions;  12  noon,  found  dead.     Autopsy:  Liver  showed  very  extensive 
coccidiosis;  no  other  lesions. 
Rabbit  421.     Belgian  hare,  male.     Weight,  1,485  grams.     Diet,  oats. 

Sejitember  2t):  10  a.  m.,  20  cc  2  per  cent  caffein  (351  mg  per  kilo)  administered  by 
mouth;  4  p.  m.,  reflexes  increased;  6  p.  m.,  reflexes  as  before,  no  tetanus  observed. 

September  27:  9  a.  m.,  rabbit  found  dead.     Autopsy:  Congestion  of  lungs  and  kid- 
neys; liver  congested  and  slightly  fatty. 
Rabbit  424.     White^male.     Weight,  1,295  grams.     Diet,  oats. 

September  2G:  2  p.  m.,  19  cc  2  per  cent  caffein  (293  mg  per  kilo)  administered  by 
mouth;  4  p.  m.,  reflexes  increasetl,  no  other  symptoms;  6  p.  m.,  no  change  since  4  p.  m. 

September  27:  12  noon,  convulsions  and  death.     Autopsy:  Congestion  of  the  lungs; 
no  other  lesions. 
Rabbit  4iS.     White,  male.     Weight,  1,205  grams.     Diet,  oats. 

September  20:  2  p.  m.,  18  cc  2  per  cent  caffein  administered  by  mouth;  4  p.  m., 
reflexes  increased,  no  tetanus;  6  p.  m.,  condition  unchanged  since  4  p.  m. 

September  27:  9  a.  m.,  found  dead.     Autopsy:  Lungs  liver,  and  kidneys  congested ; 
other  organs  normal. 
Rabbit  422.     White,  male.     Weight,  1,440  grams.     Diet,  oats. 

September  2(j:  2  p.  m.,  21  cc  2  per  cent  caffein  (291  mg  per  kilo)  given  by  mouth; 
reflexes  increased  at  4  p.  m. 

September  27:  3  p.  m.,  alive,  no  symptoms;  4  p.  m.,  convulsions  with  recovery,  this 
was  soon  followed  by  a  violent  attack  of  tetanus,  which  lasted  about  one  minute  and 
was  succeeded  by  paralysis;  rabbit  died  at  4.30.  Autopsy:  Liver  slightly  congested; 
a  small  portion  of  the  intestine  showed  congestion  and  edema;  other  organs  normal. 


28 


THE   TOXICITY    OF    CAFFEIN. 


A  study  of  these  experiments  shows  also  considerable  variation  in  the  toxicity  of 
caffein  when  given  by  mouth.  In  some  cases  a  dose  of  300  mg  per  kilo,  and  even  less, 
caused  death,  as  in  rabbits  423  and  424.  In  other  rabbits,  however,  approximately  the 
same  doses  of  caffein  produced  increased  reflexes  only.  The  same  symptoms  were  pro- 
duced in  Nos.  248  and  249  after  the  administration  of  325-330  mg  of  caffein  per  kilo, 
while  another  rabbit  (No.  239)  sur\dved  a  dose  of  363  mg  per  kilo.  That  this  is  excep- 
tional, however,  appears  from  the  result  of  the  following  experiments  on  rabbits 
Nos.  419,  420,  and  421,  all  of  which  died  after  receiving  350  mg  of  caffein  per  kilo,  and 
rabbits  267  and  268,  to  which  doses  of  363  and  342  mg,  respectively,  per  kilo  proved 
fatal.  It  will  be  observed  further  that  the  gray  rabbits  are  more  resistant  to  caffein 
than  the  white  animals,  as  350  mg  per  kilo  was  the  smallest  fatal  dose  for  rabbits  419, 
420,  and  421,  all  of  which  were  gray  rabbits,  while  a  dose  of  290  mg  per  kilo  was  fatal 
for  some  of  the  white  rabbits.  Again,  it  will  be  noticed  that  of  the  two  gray  rabbits, 
Nos.  254  and  239,  which  received  the  largest  doses  in  these  experiments,  namely,  369 
and  363  mg,  respectively,  one  survived.  The  largest  doses  given  to  the  white  rabbits 
were  363  and  342  mg  caffein  per  kilo.  Both  of  these  died  from  the  effects  of  the  drug. 
It  may  be  concluded,  therefore,  that  the  minimum  toxic  dose  for  the  gray  rabbit  is 
about  325  mg  of  caffein  per  kilo,  and  the  minimum  fatal  dose  is  at  least  350  mg  per  kilo. 
It  is  to  be  remarked  in  this  connection  that  post-mortem  examination  showed  ex- 
tensive coccidiosis  in  rabbit  420  and  fatty  liver  in  No.  421,  while  the  macroscopical 
examination  of  the  organs  of  Nos.  424  and  423  failed  to  show  the  presence  of  such 
abnormalities.  Since,  as  was  observed  in  the  section  on  subcutaneous  injection  and 
elsewhere  in  this  investigation,  pathological  changes  are  apt  to  decrease  the  resistance 
to  caffein,  it  is  quite  possible  that  350  mg  per  kilo  is  not  the  minimum  fatal  dose  for 
the  normal  rabbit.  Indeed,  the  experiment  on  rabbit  239  lends  support  to  this 
view,  thus  furnishing  additional  evidence  of  difference  in  the  resistance  to  caffein 
in  the  two  varieties  of  rabbits. 


Table  2. — Administration  of  caffein  by  mouth. 
SERIES  A. 


Rab- 
bit 
No. 

Weight. 

Caffein 
per  kilo. 

Symptoms. 

Duration  of  life. 

Diet. 

Remarks. 

248 

Grams. 

1,170 

1,380 

890 

Mg. 
330 
290 
325 

3  hours  10  minutes 

Survived 

Oats 

...do...- 

Gray. 

241 

do 

White  male. 

249 

do 

...do.... 

Gray  male. 

SERIES  B. 


239 

935 

363 

254 

975 

369 

207 

1,050 

342 

268 

1,100 

363 

419 

1,600 

350 

420 

1,250 

352 

421 

1,485 

351 

424 

1.295 

293 

423 

1,205 

300 

422 

1,440 

291 

50  minutes. 


6  hours 

1  hour  35  minutes. 
6  hours 

2  hours 

do 

do 


Survived 

About  2  days... 

1  hour  4  minutes 

About  3  hours 

Less  than  24  hours 

2  hours 

Less  than  24  hours 

22  hours 

Less  than  19  hours 
2i  hours 


INJECTION  INTO  THE  PERITONEAL  CAVITY. 

In  a  number  of  experiments  caffein  was  introduced  into  the  peritoneal  cavity. 
Rabbits  of  different  varieties  receiving  a  diet  of  oats  or  carrots  were  employed  for  this 
purpose;  food  and  water  were  given  ad  libitum.  The  minimum  doses  required  to 
induce  symptoms  or  cause  death  in  these  animals  were  determined;  tests  with  caffein 
were  also  made  on  young  rabbits  in  order  to  study  the  influence  of  age  on  the  Resistance 
to  this  substance.    The  results  are  shown  in  the  following  experiments: 


ACUTE    INTOXICATION — BABBITS.  29 

Series  A. 

In  this  series  large  dosea  were  administered,  apjiniximatinK  ()..S  Kram  per  kilo. 

RdbhitJt.    Grnij  female.     Weight,  1,659  grams. 

January  20:  2.20  p.  m.,  25  cc  aqueous  solution  2  per  cent  caffein  (300  ni^  |)er  kilo) 
were  injected  into  the  peritoneal  cavity;  3.45  p.  m.,  when  doora  of  cage  were  opened 
rabbit  had  spasm  of  short  duration. 

January  21 :  Rabbit  found  dead. 
Rabbit  7 J.     Gray  and  white.      Weight,  1,402  grams. 

January  21:  11.17  a.  m.,  20.2  vv  (acjueoiis  solution)  of  2  per  cent  caffein  (300  mg 
per  kilo)  injected  into  i)eritoneal  cavity  from  burette;  11.25  a.  m.,  paralysis;  11.30 
a.  ni.,  rabbit  had  convulsion  when  picked  up  from  the  floor,  followed  by  several 
epasms  later;  11.35  a.  m.,  typical  tetanus;  12.30  noon,  found  dead. 
Rabbit  61.     Black  female.     Weight,  2,14-3  grains. 

January  19:  40  cc  2  per  cent  caffein,  aqueous  solution  (300  mg  per  kilo),  injected 
into  peritoneal  cavity  Ironi  burette;  tetanus  when  about  30  rr  were  injected;  when 
removed  from  holder,  repeated  and  vi«jlent  convulsions,  terminating  in  death. 

Series  B. 

The  object  of  these  experiments  was  to  determine  the  minimum  lethal  dose;  0.2  to 
0.15  gram  of  caffein  per  kilo  was  injected  into  the  rabbits  of  this  series. 

Rabbit  69.     White  female.     Weight,  1,714  grams. 

January  20:  10.15  a.  m.,  (i  cc  2  per  cent  caffein,  aqueous  solution,  injected  into 
peritoneal  cavity.  No  symptoms,  under  observation  for  45  minutes,  rabbit  defecated 
rather  copiously;  feces  were  soft;  11  a.  m.,  6  cc  2  per  cent  caffein,  aqueous  solution, 
injec-ted  into  peritoneal  cavity,  no  symptoms,  under  observation  for  40  minutes;  11.40, 
6  cc  2  per  cent  caffein  injected  into  peritoneal  cavity;  11.45,  rabbit  is  restless,  reflexes 
increased. 
Rabbit  70.    Gray  and  white  female.     Weight,  1,487  grams. 

January  20:  1.30  p.  m.,  15  cc  2  per  cent  aqueous  solution  of  caffein  (0.2  gram  per 
kilo)  injected  into  the  peritoneal  cavity;  2.20  p.  m.,  no  symptoms. 

January  30:  About  2  p.  m.  rabbit  died. 

February  1:  Autopsy:  Cirrhosis  of  the  liver;  enteritis  of  small  intestines;  stomach 
and  kidneys  normal. 
Rabbit  93.     Maltese,  male.     Weight,  1,197  grams. 

March  2:  11.30  a.  m.,  12  cc  of  2  per  cent  caffein  (200  mg  per  kilo)  injected  into 
peritoneal  cavity;  11.35  a.  m.,  while  being  released  from  holder,  tetanus  occurred, 
repeated  attacks  later,  clonic  convulsions  with  tonic  rigidity  of  posterior  extremities 
during  the  attacks  as  well  as  during  intervals,  anterior  extremities  were  relaxed  during 
the  intervals  between  the  attacks,  opisthotonos  of  cervical  region  but  kyphosis  in 
lumbar  region  were  observed,  no  salivation  nor  dilatation  of  the  pupils;  2  p.  m., 
rabbit  died. 

Rabbit  92.      Yellow  female.     Weight,  1,388  grams. 

February  25,  4.15  p.  m.,  14  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  into 
peritoneal  cavity;  4.20  p.  m.,  restlessness  and  increased  reflexes,  rabbit  found  stretched 
out  in  cage,  but  raised  himself  on  his  legs  again;  4.45,  general  tremor  when  touched. 

February  26:  9  a.  m.,  rabbit  found  dead.     Autopsy:  Hemorrhage  into  abdominal 
muscles  at  site   of   injection;  hemorrhage  also  in  walls  of  stomach  opposite  similar 
spot  in  abdominal  wall. 
Rabbit, 309.     Belgian  hare,  female.     Weight,  1,. 500  grams.     Diet,  oats. 

March  2:  2.05  p.  m.,  2per  cent  caffein  solution  (0.2  gram  per  kilo)  injected  into 
peritoneal  cavity;  2.25  p.  m.,  found  dead,  no  urine  found  in  bladder. 
Rabbit  307.     Belgian  hare,  female.     Weight,  1,320  grams.     Diet,  oats. 

March  2:  12  noon,  urine  obtained  from  bladder,  clear  amber  colored,  no  albumin, 
no  reduction;  12.06  p.  m.,  10  cc  of  2  per  cent  caffein  (0.151  gram  per  kilo)  injected 
into  peritoneal  cavity;  1.30  p.  m.,  rabbit  ])laced  on  floor,  runs  around  but  anterior  and 
posterior  extremities  soon  extended,  in  tonic  condition;  2.25  p.  m.,  reflexes  increased, 
paralysis  of  extremities,  dyspnoea;  4.50  p.  m.,  about  100  cc  urine  collected,  no 
albumin,  reduction  of  Fchling's  solution  moderate. 

March  3:  9.30  a.  m.,  posterior  extremities  extended  and  rigid,  anterior  extremities 
paralyzed,  respiration  less  frequent  and  deeper  than  normal.  Rabbit  died  at  11.50 
a.  m.;  urine  collected  since  4.50  p.  m.  previous  day  gave  very  heavy  reduction  of 
Fehling's  solution.    Autopsy:  Animal  in  good  condition;  in  the  left  axillary  region 


30  THE   TOXICITY   OF   CAFFEIN. 

was  observed  a  hemorrhage  into  the  subcutaneous  and  muscular  tissue  of  that  region. 
The  ventral  portion  of  the  large  colon,  in  contact  with  the  ventral  abdominal  wall, 
showed  a  hemorrhagic  area  about  one-half  inch  in  length,  such  as  might  be  produced 
by  a  puncture  or  bruise  of  the  colon  through  the  abdominal  wall.  A  small  portion 
of  the  small  intestine  adjacent  to  the  colon  was  affected  in  a  similar  manner.  All 
internal  organs  were  apparently  normal. 
Rabbit  308.    Belgian  hare,  female.     Weight,  1,350  grams.    Diet,  oats. 

March  2:  11.45  a.  m.,  urine  obtained  from  bladder,  no  albumen,  no  reduction; 
11.50  a.  m.,  10  cc  2  per  cent  caffein  (0.15  gram  per  kilo)  injected  into  peritoneal  cav- 
ity; 1.30  p.  m.,  not  very  active,  no  abnormal  symptoms  otherwise;  3.  30  p.  m.,  rabbit 
looked  depressed,  made  very  little  attempt  to  move  about,  remained  in  one  position 
most  of  the  time  when  placed  on  floor;  4.30  p.  m.,  180  cc  m-ine  collected,  no  albumen, 
reduction  of  Fehling's  solution  moderate. 

March  3:  9.30  a.  m.,  rabbit  looks  normal,  is  able  to  walk  but  is  easily  fatigued  when 
made  to  walk  about  or  when  placed  on  his  side,  followed  by  paralysis  of  anterior 
extremities,  posterior  extremities  apparently  normal,  about  90  cc  of  urine  collected 
at  noon  was  free  from  albumen,  did  not  reduce  Fehling's  solution. 

March  4:  11  a.  m.,  lying  on  his  side  in  cage,  anterior  extremities  limp,  posterior 
extremities  extended  and  rigid,  is  in  dying  condition. 

March  5:  9  a.  m.,  found  dead.  Autopsy:  Liver  engorged;  spleen  congested,  but 
not  enlarged;  kidneys,  some  congestion  in  cortex;  stomach  filled,  mucosa  thickened 
and  easily  pulled  off;  petechial  hemorrhages  on  serosa  of  colon. 

Series  C. 

The  experiments  of  this  series  were  made  to  determine  the  minimum  toxic  dose. 
Rabbit  295.     Belgian  hare,  female.     Weight,  1,205  grams.    Diet,  carrots. 

March  1:  10.40  a.  m.,  6  cc  2  per  cent  caffein  (0.1  gram  per  kilo)  injected  into  peri- 
toneal ca^^ty;  about  2  cc  of  urine  obtained  before  injecting  caffein;  2  p.  m,  100  cc 
urine,  bloody  in  appearance,  collected,  a  moderate  quantity  of  albumen  present,  no 
reduction;  3.40  p.  m.,  no  symptoms. 

March  4:  2  p.  m.,  rabbit  looks  well. 
Rabbit  293.     Belgian  hare,  female.     Weight,  1,605  grams.    Diet,  carrots. 

March  1:  Urine  from  bladder  clear,  alkaline;  11.55  a.  m.,  8  cc  2  per  cent  caffein 
(0.1  gram  per  kilo)  injected  into  peritoneal  cavity;  3  p.  m.,  90  cc  urine  normal  in  color 
collected,  no  albumen,  no  reduction;  3.40  p.  m.,  no  symptoms. 

March  4:  1.15  p.  m.,  rabbit  looks  normal. 
Rabbit  292.    Belgian  hare,  male.     Weight,  1,595  grams    Diet,  carrots. 

March  1:  10.10  a.  m.,  8  cc  2  per  cent  caffein  (0.1  gram  per  kilo)  solution  injected 
into  peritoneal  cavity;  10.40  a.  m.,  rabbit  lu-inated,  reflexes  increased,  but  no  other 
symptoms;  10.50  a.  m.,  no  urine  obtained  from  bladder;  2  p.  m.,  105  cc  of  clear  pale 
urine  collected;  no  albumen,  no  reduction;  3.40  p.  m.,  no  symptoms. 

March  4:  2  p.  m.,  rabbit  looks  well,  mine  collected,  did  not  contain  sugar. 
Rabbit  298.     Belgian  hare,  female.     Weight,  1,205  grams.     Diet,  carrots. 

March  1:  4.06  p.  m.,'  7.5  cc  2  per  cent  caffein  solution  (0.125  gram  per  kilo)  iiijected 
into  peritoneal  cavity,  urine  obtained  from  bladder  immediately  after  injection,  no 
albumen,  no  reduction;  5.30  p.  m.,  reflexes  increased,  rabbit  was  able  to  run  around, 
but  became  paralyzed  soon;  5.40  p.  m.,  rabbit  is  again  able  to  run  arouud. 

March  3:  10  a,,  m.,  anterior  extremities  paralyzed,  is  able  to  use  posterior  exkemi- 
ties. 

March  4:  1  p.  m.,  rabbit  looks  normal. 
Rabbit  223.     Belgian  hare,  male.     Weight,  1,165  grams.     Di£t,  carrots. 

March  1:  3.50  p.  m.,  urine  obtained  from  bladder  clear,  amber  colored,  no  albumeii, 
no  sugar;  3.52  p.  m.,  7.5  cc  2  per  cent  caffein  (125  mg  per  kilo)  injected  into  peri- 
toneal cavity;  5.40  p.  m.,  rabbit  makes  little  attempt  to  run  when  put  on  the  floor, 
weakness  of  extremities  marked. 

March  4:  1.15  p.  m.,  rabbit  normal. 

Series  D. 

The  object  of  the  experiments  of  this  series  was  to  study  the  effect  of  age  on  the 
resistance  to  caffein.     Half-grown  rabbits  were,  therefore,  used  in  the  following  experi- 
ments. 
Rabbit  310.     Belgian  hare,  female.     Weight,  880  gr&Tns.     Diet,  oats. 

March  2:  3.25  p.  m.,  9  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  into  peri- 
toneal cavity. 


ACUTE   INTOXICATION — RABBITS.  31 

March  3:  9.30  a.  m.,  no  symptoms,  rabbit  looks  normal. 

March  4:  II  a.  m.,  posterior  extremities  abductetl,  walked  when  placed  on  the 
fl(K)r,  made  no  attempt  to  change  attitude  when  placed  on  it.s  side,  remained  some 
time  in  this  position. 

March  5:  9  a.  m.,  found  dead.    Autopsy:  Liver  showed  areas  of  degeneration; 
kidneys  cong&^tion  and  petechial  hemorrhage  on  cortex;  small  and  large  intestines, 
inflammation  marked;  bladder  distended. 
Rabbit  75.    Gray  arid  irhite,  female.     Weight,  842  grains. 

January  25:  3  p.  m.,  8.5  cc  2  per  cent  caffein  solution  (0.2  gram  per  kilo)  injected 
into  peritoneal  cavity;  3.15  p.  m.,  anterior  extremities  weak  and  reflexes  increased. 

January  27:  Rabbit  paralyzed  but  is  able  to  turn  over  when  placed  on  back. 
Rabbit  74.    Gray  and  uhite,  female.     Weight,  692  grams. 

January  25:  3  p.  m.,  7  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  solution  injected 
into  |>eritoneal  cavity;  3.15  p.  m.,  reflexes  increased  and  anterior  extremities  paralyzed. 

January  27:  Rabbit  recovered  and  is  able  to  walk  about  in  the  room. 
Rabbit  S 1 2,  maltese,  female.     Weight,  740  gn.m^.     Diet,  oats. 

March  3:  11.47  a.  m.,  urine  obtained  from  bladder,  appearance  normal,  no  albumen, 
no  reduction  of  Fehling's  solution;  1 1.50  a.  m.,  7.5  cc  2  per  cent  caffein  (0.2  gram  per 
kilo)  injected  into  peritoneal  cavity;  2.30  p.  m.  anterior  extremities  paralyzed,  pos- 
terior extremities  rigid  and  extended;  5  p.  m.  (about),  rabbit  died. 
Rabbit  311.     Belgian  hare,  female.     Weight,  6-50  grams.     Diet,  oats. 

March  3:  11.26  a.  m.,  lu-ine  obtained  from  bladder  normal  in  appearance,  albumen 
considerable,  reduction  of  Fehling's  solution  none;  11.27  a.  m.,  6  cc  2  per  cent  caffein 
Bolution  (0.2  gram  per  kilo)  injected  into  peritoneal  cavity;  2.30  p.  m.,  rabbit  seemed 
to  be  normal,  no  symptoms  had  developed;  urine  collected  contained  a  large  amount 
of  sugar,  reduction  was  very  heavy,  but  no  albumen  was  found. 

March  4:  11  a.  m.,  condition  good,  moves  about  when  put  on  floor;  gait,  normal. 
Rabbit  78.      Yelloiv  and  uhite.     Weight  659  grams. 

January  26:  1.30  p.  m.,  8.5  cc  2  per  cent  caffein  (250  mg  per  kilo)  injected  into 
peritoneal  cavity,  under  obser\-ation  the  rest  of  the  afternoon,  no  symptoms. 

January  27:  4  p.  m..  no  sj-mptoms  developed. 
Rabbit  S17.     Belgian  hare,  female.     Weight  635  gravis.     Diet  oafs. 

March  15:  10.35  a.  m.,  8  cc  2  per  cent  caffein  (0.  252  gram  per  kilo)  injected  into 
peritoneal  cavity;  12  noon,  marked  abduction  of  hind  legs,  was  unable  to  walk  after 
a  little  exertion,  rabbit  died  between  12.30  and  12.50  p.  m.  Autopsy.  Right  lung 
hepatized  and  showed  adhesions  to  costal  and  mediastinal  pleura;  liver  studded 
with  nodules  of  coccidiosis;  spleen  congested;  stomach  tilled,  mucosa  normal;  intes- 
tines injected:  colon  hemorrhagic  on  serosa  in  ventral  region,  near  point  of  injection; 
kidneys  normal. 
Rabbit  323.     White,  female.     Weight  820  grams.    Diet  oats. 

Jklarch  15:  10.45  a.  m.,  10  cc  2  j^er  cent  caffein  (250  mg  per  kilo)  injected  into  peri- 
toneal cavity;  12  noon,  reflexes  increased,  hind  legs  abducted  but  is  able  to  walk, 
BjTnptoras  are  mild:  1.40  p.  m.,  tremors,  weakness,  and  abduction  of  head  and  legs 
much  more  marked  than  at  12  noon. 

March  16:  Condition  good. 

March  17:  Condition  good,  recovery  apparently  complete. 

Since  the  experiments  of  Series  A,  which  were  intended  as  preliminary  tests,  have 
shown  that  0.3  gram  of  caffein  per  kilo  when  introduced  into  the  peritoneal  cavity  is 
rapidly  absorbed  and  is  fatal,  much  smaller  (ioses  were  employed  in  subsequent 
trials  with  the  drug.  This  is  shown  in  series  B,  which  may  be  divided  into  two 
groups.  Group  I,  consisting  of  rabbits  69,  70,  92,  93,  and  309,  which  received  0.2 
gram  of  caffein  per  kilo,  and  Group  II,  Nos.  307  and  308,  into  which  0.15  gram  of 
caffein  per  kilo  was  injected.  Three  rabbits  of  Group  I  (Nos.  92,  93,  309)  died  from 
the  effects  of  caffein;  rabbit  309  twenty  minutes  after  injection,  and  rabbits  Nos.  92 
and  93,  twenty  hoiu-s  and  two  and  one-half  hoiu-s.  respectively,  after  the  administration 
[Of  caffein.  In  both  of  these  rabbits  svanptoms  appeared  within  five  minutes  after  the 
injections  were  made.  Rabbits  69  and  70,  it  will  be  noticed,  survived  the  same 
amount  of  caffein  in  proportion  to  body  weight  as  was  given  to  the  other  members  of 
this  group.  Increased  peristalsis  and  the  distribution  of  the  dose  may  account  for  the 
greater  resistance  of  rabbit  No.  69.  The  case  of  rabbit  No.  70  is  evidently  one  of  ex- 
ceptional resistance  to  caffein,  since  both  the  rabbits  of  Group  II  died  from  the  effects 


32 


THE    TOXICITY    OF    CAFFEIN. 


of  a  much  smaller  dose,  namely,  0. 15  gram  of  caff ein  per  kilo.  Moreover,  macroscopical 
examination  at  the  autopsy  of  Nos.  307  and  308  failed  to  show  any  lesions  which  might 
tend  to  lessen  the  resistance  to  caff  ein. 

That  a  dose  of  0.15  gram  per  kilo  is  therefore  in  all  probability  the  minimum  fatal 
dose  for  the  rabbit  when  injected  into  the  peritoneal  cavity  appears  from  the  results 
of  the  experiments  in  series  C,  in  which  smaller  doses,  0.125  gram  of  caffein  per  kilo 
caused  mild  symptoms  only,  while  0.1  gram  per  kilo  rarely  induced  any  symptoms. 
It  may  be  remarked  that  the  rabbits  of  series  C  were  fed  carrots  while  rabbits  Nos.  307 
and  308  received  oats.  Their- resistance  to  caffein  may  be  different,  but,  as  was 
pointed  out  in  the  earlier  part  of  this  investigation,  diet  does  not  seem  to  influence  the 
toxicity  of  the  single  dose  of  caffein.  Doses  of  150  and  of  100  to  125  mg  per  kilo,  when 
injected  into  the  peritoneal  cavity,  may  be  considered,  respectively,  as  the  minimum 
fatal  and  minimum  toxic  doses  for  the  gray  rabbit.  Analysis  of  the  experiments  in 
series  D  shows  much  greater  resistance  to  caffein  than  in  the  other  rabbits  which 
received  it  intraperitoneally.  Thus,  after  the  administration  of  0.2  gram  per  kilo  to 
each  of  five  rabbits,  no  effect  was  observed  in  two  cases  (Nos.  310,  311),  while  in  two 
others  (Nos.  74,  75)  symptoms  developed,  but  they  survived.  Only  one  rabbit,  No- 
312,  died  from  the  effects  of  this  dose;  the  autopsy  showed  the  presence  of  degenera- 
tion of  the  liver  and  petechial  hemorrhages  on  the  cortex  of  the  kidneys  in  the  case  of 
No.  310,  which  was  probably  the  cause  of  death  rather  than  the  caffein. 

Two  decigrams  of  caffein  can  not  be  considered,  therefore,  the  fatal  dose  for  rabbits. 
This  is  further  corroborated  by  the  results  obtained  in  experiments  Avith  larger  doses. 
Rabbit  78,  which  received  257  mg  per  kilo,  failed  to  show  any  symptoms.  The  same 
amount  in  proportion  to  body  weight  in  No.  323  caused  mild  symptoms  only,  while 
the  rapid  death  of  rabbit  No.  317  after  the  same  dose  of  caffein  may  be  explained  by  the 
lesion  found  at  autopsy,  thus  affording  additional  evidence  that  disease  may  decrease 
the  resistance  to  caffein.  It  will  be  observed  that  all  the  members  of  this  series  were 
young  rabbits  and,  as  will  be  shown  later,  young  animals  of  other  species  are  likewise 
more  resistant  to  caffein  than  adult  animals.  Similar  results  were  obtained  by  von' 
Anrep,  Avho  observed  that  atropin  is  less  toxic  in  young  than  in  full-grown  animals. 

Observations  were  also  made  on  the  diuretic  effect  of  caffein  when  injected  into  the 
peritoneal  cavity.  The  results  shown  in  the  following  table  indicates  the  stimulating 
effect  on  renal  secretion  whether  the  diet  consisted  of  oats  or  of  carrots.  The  urine  of 
some  rabbits  contained  moderate  amounts  of  sugar  after  from  0.2  to  0.15  gram  of  caffein 
per  kilo  was  given;  albumen  was  observed  in  one  case,  but  in  none  of  the  others.  In 
rabbit  No.  311  albumin  was  found  before  the  injection  of  caffein,  but  none  in  the  urine 
which  was  collected  three  hours  after  caffein  was  injected. 

Effect  of  caffein  on  renal  secretion. 


No. 

Weight. 

Caffein 
per  kilo. 

Urine. 

Time. 

Diet. 

307 

Grams. 
1,320 
1,.305 
1,205 

1,605 
1,595 

Gram. 
0.150 
.150 
.100 

.100 
.100 

cc. 
100 
180 
100 

90 
105 

1.5  liours 

do 

2  hours  20  min- 

utes. 

3  hours 

4  hours 

Oats. 

308 

Do. 

295 

Carrots. 

293       .                                                    .... 

Do. 

292 

Do. 

Note.— The  amount  pf  urine  secreted  in  three  hours  by  control  rabbits,  on  a  carrot  diet,  varied  between 
.3.5  and  .50  cc,  the  average  weight  of  the  animals  being  a  little  above  1,600  grams.  The  secretion  of  urine 
on  an  oat  diet  was  much  less  for  an  equal  period  of  time. 


ACUTE   INTOXICATION — RABBITS. 


33 


Table  3. — Intraperitoneal  injections. 
SERIES  A. 


No. 

Weight. 

C'aflein 
per  kilo. 

Time  of  appearance  of 
symptoms. 

Duration  of  life. 

Remarks. 

71 

Grams. 
1,659 
2,113 
1,402 

Oram. 
0.3 
.3 
.3 

24  hours 

Gray. 
Black. 

61 

At  the  end  of  injection . . 
1.25  hour 

72 

Gray  and  white. 

SERIES  B,  group:. 


70 

1,4S7 
1,492 

1,492 
1,388 
1,500 

0.2 

.2 

.2 
.2 

10  (lavs 

Gray  and  white. 
Maltese;     given    second 

93 

2.')  hours 

69 

About  5  minutes 

Survived 

dose  after  3  days,  died 
2.5  hours  later. 
White. 

92 

24  hours 

Yellow. 

309 

20  minutes 

Belgian;  oats. 

SERIES   B,   GROUP  II. 


0.15 
.15 


3  hours  and  40  minutes. 
1  hour  24  minutes 


About  2.5  days. 
24  hours 


Belgian;  oats. 
Do. 


SERIES  C. 


223 
293 
295 
292 
298 


1,16.5 

0.125 

1,605 

.1 

1.205 

.1 

1,595 

.1 

1,205 

.125 

2  hours. 


1.5  hours. 


Survived. 

do... 

do... 

do... 

do... 


Belgian;  carrots. 

Do". 
Do. 
Do. 


SERIES   D. 


310 

311 

312 

78 

75 

74 

317 

323 


880 

0.2 

650 

.2 

740 

.2 

659 

.257 

842 

.2 

C.92 

.2 

63.1 

.252 

820 

.25 

2  days  1 


40  minutes , 

15  minutes , 

do 

do 

1  hour  25  minutes  . 
1  hour  15  minutes  , 


About  2.5  days'. 

Survived 

4.5  hours 

Survived 

do 

do 

About  2  hours . . . 
Survived 


Belgian;  oats. 

Do. 
Maltese;  oats. 
Yellow  and  white;  oats. 
Gray  and  white. 

Belgian;  oats. 
White;  oats. 


>  Not  due  to  caflfein. 


INTRAMUSCTJIiAR  INJECTION. 

Well-fed  rabbits,  which  received  a  diet  exclusively  of  oats,  were  used  for  these 
experiments.    The  injections  were  made  into  the  lumbar  or  into  the  gluteal  muscles. 

Series  A. 

In  this  series  the  caffein  was  injected  into  the  gluteal  muscles. 

Rabbit  284.    Brotcn  and  white,  female.     Weight,  1,100  grams. 

December  14:  2  p.  m.,  11  cc  2  per  cent  caffein  injected  into  the  gluteal  muscles 
(0.2  gram  per  kilo),  under  observation  until  5  p.  ni.,  had  frequent  convulsions;  at 
5  p.  m.  in  a  comatose  condition.     Rabbit  was  found  dead  the  next  morning. 
Rabbit  2S6,  while  and  black,  female.     Weight,  1,31.5  grams. 

December  15:  2.30  p.  m.,  13  cc  2  per  cent  caffein  injected  into  the  gluteal  muscles 
(0.1977  gram  per  kilo),  tremors  and  increased  reflexes  observed  during  the  next  two 
hours,  but  no  other  symptoms. 

December  17:  Rabbit  alive. 

18594°— Bull.  148—12 3 


34  THE   TOXICITY   OF    CAFFEIN. 

Rabbit  2S5,  yelloiv  and  tvhite,  female.     Weight,  1,385  grams. 

December  14:  10.15  a.  m.,  14  cc  2  per  cent  caffein  injected  into  the  gluteal  muscles 
(0.2  gram  per  kilo),  general  tremors,  but  no  convulsions  observed.     Rabbit  survived. 

December  17 :  Rabbit  still  alive. 
Rabbit  287.    Belgian  hare,  female.     Weight,  1,140  grams. 

December  15:  2.15  p.m.,  lice  of  2  per  cent  caffein  injected  into  the  gluteal  muscles; 
2.30  p.  m.,  tonic  contractions  of  posterior  limbs.     Paralysis  and  death  at  2.40  p.m. 

Series  B. 

In  series  B  the  caffein  was  injected  into  the  lumbar  muscles. 

Rabbit  307.    Belgian  hare,  female.     Weight,  1,175  grams. 

February  16:  11.05  a.  m.,  8  cc  2  per  cent  caffein  injected  (0.136  gram  per  kilo)  into 
the  lumbar  muscles;  under  observation  until  4  p.  m.,  no  symptoms;  4  p.m.,  allowed 
to  walk  on  the  floor;  after  walking  a  short  distance  loss  of  coordination  and  paralysis 
of  posterior  extremities;  5.20  p.  m.,  found  dead. 
Rabbit  306.     Belgian  hare,  female.     Weight,  1,860  grams. 

February  16:  11  a.  m.,  12.5  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles; 
12  noon,  no  symptoms;  2  p.  m.,  walked  about  10  feet,  exhaustion  and  paralysis; 
3p.m.  found  dead. 

Rabbit  181.    Belgian   hare.     Weight,    1,230    grams.     (Was    experimented    on    some 
time  previously.) 

February  16:  10.55  a.  m.,  8  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles; 
(0.130  gram  per  kilo);  12  noon,  no  symptoms;  2  p.  m.,  no  symptoms;  3  p.  m.,  put  on 
the  floor,  walked  about  10  feet  and  was  exhausted,  posterior  extremities  paralyzed; 
4  p.  m.,  found  dead. 

Series  C. 

In  the  fall  of  the  same  year  additional  experiments  were  carried  out  with  doses 
ranging  from  100  to  200  milligrams  of  caffein  per  kilo,  which  were  injected  into  the 
lumbar  muscles.     The  results  are  given  in  the  following  abbreviated  protocols: 

Rabbit  425.    Belgian  hare.     Weight  1,520  grams. 

September  27:  10.30  a.  m.,  7.5  cc  2  per  cent  caffein  injected  into  the  lumbar  mus- 
cles; 2  p.  m.,  reflexes  increased. 

September  28:  Rabbit  normal. 

October  5:  Weight,  1,620  grams;  2.50  p.  m.,  10  cc  2  per  cent  caffein  injected  into 
lumbar  muscles;  3.05  p.  m.,  reflexes  increased. 

October  13:  Weight,  1,520  grams;  10.30  a.  m.,  10  cc  2  per  cent  caffein  (131  mg  per 
kilo)  injected;  11  a.  m.,  no  symptoms;  11.30  a.  m.,  reflexes  much  increased. 

October  14:  Alive,  no  symptoms. 
Rabbit  426.    Belgian  hare,  female.     Weight,  1,425  grams. 

September  27 :  7  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles  at  10.30  a.  m.; 
2  p.  m.,  reflexes  increased. 

September  28:  Rabbit  normal. 

October  5:  Weight,  1,425  grams;  2.55  p.m.,  9  cc  2  per  cent  caffein  injected  into  lum- 
bar muscles;  3.05  p.  m.,  reflexes  increased. 

October  13:  Weight,  1,405  grams;  10.30  a.  m.,  10  cc  2  per  cent  caffein  (142  mg  per 
kilo)  injected;  11  a.  m.,  no  symptoms;  11.30  a.  m.,  reflexes  increased. 

October  14:  Rabbit  alive,  no  symptoms. 
Rabbit  427.    Belgian  hare,  female.     Weight,  1,780  grams. 

September  27:  9  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles;  2  p.  m., 
reflexes  increased. 

September  28:  Rabbit  normal. 

October  5:  Weight,  1,  850  grams;  3  p.  m.,  11.5  cc  2  per  cent  caffein  injected  into 
lumbar  muscles;  3.10  p.  m.,  reflexes  increased. 

October  13:  Weight,  1,830  grams;  10.40  a.  m.,  14  cc  2  per  cent  caffein  (153  mg  per 
kilo)  injected  into  lumbar  muscles;  11  a.  m.,  no  symptoms;  11.30  a.  m.,  reflexes 
increased. 

October  14:  Rabbit  alive,  no  symptoms. 
Rabbit  453.    Belgian  hare,  male.     Weight,  1,160  grams. 

October  12:  3.45  p.  m.,  11.5  cc  2  per  cent  caffein  in  aqueous  solution  injected  into 
lumbar  muscles;  4.15  p.  m.,  reflexes  increased;  4.30  p.  m.,  paralyzed. 


ACUTE  INTOXICATION — RABBITS.  35 

October  13:  9  a.  m.,  found  dead.     Autopsy:  Gastric  mucosa  hemorrhagic;  liver 
darkened;  other  organs  normal. 
Rabbit  45'} .     Belgian  hire,  gray,  female.      Weight,  1,185  grams. 

October  12:  ;i.:iO  p.  m.,  11.5  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles; 
4  p.  m.,  reflexes  increased. 

October  13:  Rabbit  weighed  1,070  grams,  no  symptom  of  caffein  poisoning,  rcflcxea 
normal;  10.30  a.  m.,  10  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles;  11.30 
a.  m.,  jumped  off  the  tiible,  had  attack  of  convulsions  and  died.     Autopsy:  Findings 
same  as  in  No.  453. 
Babbit  428.     Belgian  hare,  gray,  male.      Weight,  1,650  grams. 

October  5:  4  p.  m.,  14.8  cc  2  percent  caffein  (0.18  gram  per  kilo)  injected  into  the 
lumbar  muscles. 

October  G:  Found  dead. 
Rabbit  429.     Belgian  hare,  male.     Weight,  1,. 340  grams. 

October  5:  4  p.  m.,  13.5  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  into  lum- 
bar muscles. 

October  8:  Rabbit  found  dead. 

Series  D. 

Further  experimenks  making  injections  into  both  the  lumbar  and  the  gluteal  muscles, 
were  made  in  this  series. 

Rabbit  577.    Gray  male.     Weight,  1,380  grams. 

February  14:  3  p.  m.  14  cc  2  per  cent  caffein  injected  into  the  gluteal  muscles  of 

'  the  right  side;  3.10  p.  m.,  restless,  jumped  off  the  table  and  walked  about,  reflexes 

increased;  3.45  p.  m.,  passed  30  cc  clear,  straw-colored  urine;  4.45  p.  m.,  allowed  to 

walk  about,  ran  across  the  room,  about  20  feet,  looked  tired,  stretched  himself  out  on 

the  floor,  then  raised  himself  and  walked  about  showing  no  disturbance  of  gait. 

February  15:  9  a.  m.,  found  dead. 
Rabbit  578.    Gray,  female.     Weight,  1,670  gram^. 

February  14:  3.05  p.  m.,  18  cc  2  per  cent  caffein  solution  injected  into  the  gluteal 
muscles  of  the  right  side;  3.15  reflexes  increased,  but  not  restless;  5  p.  m.,  allowed  to 
walk  about,  no  symptoms  observed. 

February  15:  Found  dead. 
Rabbit  579.     White  and  gray,  male.     Weight,  1,490  grams. 

February  14:  3.15  p.  m.,  15  cc  2  per  cent  caffein  solution  injected  into  the  gluteal 
muscles  of  the  right  side,  put  in  cage;  3.30  p.  m.,  reflexes  increased;  5  p.  m.,  taken 
out  of  cage  and  allowed  to  walk  across  the  room,  no  special  symptoms  noticed. 

February  23:  Still  alive. 
Rabbit  580.    Gray  male.     Weight,  1,510  gram^. 

February  14:  3.35  p.  m.,  15  cc  2  per  cent  caffein  solution  injected  into  lumbar 
muscles. 

February  23:  Still  alive,  in  good  condition. 
Rabbit  581.    Gray  female.     Weight,  1,680  grams. 

February  14:  3.45  p.  m.,  17  cc  2  per  cent  caffein  solution  injected  into  the  lumbar 
muscles  of  the  right  side;  4  p.  m.,  reflexes  increased;  4.15  p.  m.,  jumped  off  the  table 
and  had  wild  convulsions,  became  very  restless,  walked  about  the  laboratory;  4.25 
p.  m.,  had  convulsions  occasionally;  4.30  p.  m.,  extremities  extended  and  quite  rigid; 
4.35  p.  m.,  convulsions  and  death. 
Rabbit  582.    Gray  male.     Weight,  1,870  grams. 

February  14:  4.15  p.  m.,  18  cc  2  per  cent  caffein  solution  injected  into  the  lumbar 
muscles  of  right  side;  5  p.  m.,  reflexes  increased;  walked  about  in  the  room,  then 
rested;  5.15  p.  m.,  had  short  spasm  when  handled. 

February  23:  Alive;  good  condition. 

The  data  presented  in  these  experiments  show  that  the  toxicity  of  caffein  when 
injected  into  the  muscles  of  the  lumbar  regions  is  the  same  as  when  injected  into  the 
gluteal  muscles.  The  rabbits  of  series  A  received  approximately  0.2  gram  caffein  per 
kilo  and  two  died  as  a  result  of  this  treatment.  The  other  two  sur\'ived  but  symptoms 
of  caffein  intoxication  were  observed. 

In  series  B  smaller  doses  proved  fatal,  from  which  it  would  appear  that  caffein  is 
more  toxic  when  injected  into  the  lumbar  muscles.  Further  observation?,  however, 
failed  to  corroborate  the  results  obtained  in  this  series.     Thus,  in  series  C,  130  to  150 


36 


THE   TOXICITY   OF   CAFFEIN. 


mg  of  caifein  per  kilo  injected  into  the  lumbar  muscles  produced  mild  symptoms  only. 
Experiments  with  larger  doses  showed  that  0.180  gram  caffein  per  kilo  may  cause 
death.  It  will  be  noticed,  on  the  other  hand,  that  rabbit  No.  455  survived  a  dose  of 
0.2  gram  per  kilo.  New  experiments  were  therefore  carried  out  in  which  the  same 
amounts  of  caffein  in  proportion  to  the  weight  of  the  animals  were  injected  into  the 
lumbar  muscles  as  into  the  gluteal  muscles.  As  shown  in  the  experiments  of  series  D, 
one  rabbit  (No.  581)  died  shortly  after  caffein  was  injected  into  the  lumbar  muscles; 
two  recovered.  Two  of  the  three  which  received  injections  into  the  gluteal  muscles 
were  found  dead  the  next  day;  one  recovered.  Post-mortem  examination  failed  to 
indicate  the  presence  of  any  abnormalities.  The  rate  of  absorption  of  caffein  from 
the  gluteal  and  from  the  lumbar  muscles  seems  to  be,  therefore,  the  same,  or  not  to 
differ  very  much .  The  observations  of  Auer  and  Meltzer''  are  of  interest  in  this  con- 
nection. According  to  their  investigations  adrenalin  is  more  rapidly  absorbed  from 
the  lumbar  than  from  the  gluteal  muscles.  This  is  in  all  probability  due  to  the  greater 
delicacy  of  the  test  they  employed  (since  they  judged  the  rate  of  absorption  by  the 
effect  of  adrenalin  on  blood  pressure)  as  well  as  to  the  much  greater  activity  of  the 
substance. 

Table  4. — Intramuscular  injections. 

SERIES  A. 


No. 

Weight. 

Caffein 
per 
kilo. 

Symptoms 
after— 

Duration  of  life. 

Site  of  in- 
jection. 

Remarks. 

284 
286 

Grams. 
1,100 
1,315 

1,38.5 
1,140 

Gram. 

0.200 
.1977 
.200 
.210 

3  hours 

2hoiu-s 

Less  than 20 hours... 

Gluteal... 
...do 

White  and  brown  female. 
White  and  black  female. 

285 

do          

...do 

Yellow  and  white  female. 

287 

15  minutes 

25  minutes 

...do 

Gray  female. 

SERIES  B. 


307 

30fi 

1,175 

i,8eo 

1,230 

0.136 
.134 
.130 

5  hours 

3  hours 

4  hours 

6  hours,  20  minutes... 
4  hours 

Lumbar... 
...do 

Grayfemale. 
Gray. 

1S1 

...do 

SERIES  C. 


425 

1,520 
1,405 
1,830 
1,160 
1,185 
1,6.50 
1,340 

0.131 
.142 
.  153 
.200 
.200 
.180 
.200 

1  hour 

30  minutes 

50  minutes 

30  minutes 

do 

Survived 

Lumbar... 
...do 

Gray. 

426 

do 

Grayfemalo. 

427 

do    

...do 

453 
455 

Less  than  20  hours. . . 
Survived 

...do 

...do 

Gray  male. 
Gray  female. 

428 

Le.ss  than  20  hours. . . 
do 

...do 

...do 

Gray  male. 

429 



Do. 

SERIES  D. 


577 

1,380 

0.200 

578 

1,070 

.210 

579 

1,490 

.200 

.580 

1,510 

.200 

581 

1,080 

.200 

582 

1,870 

.192 

10  minutes 

do 

15  minutes 


15  minutes 
45  minutes 


Less  than  18  hours. . . 

do 

Survived 

do 

50  minutes 

Survived 


Gluteal.. 

..do 

..do 

Lumbar. 

..do 

..do 


Gray  male. 

White  and  gray  male. 
Gray  male. 

iDo. 

Do. 


Examination  of  Table  4  shows  that  14  rabbits  received  from  180  to  210  mg  caffein 
per  kilo.  The  appearance  of  symptoms  in  these  rabbits  varied  considerably.  In 
some  increased  reflexes  could  be  noticed  in  10  to  15  minutes  after  the  injection  of 
caffein;  in  others  it  was  delayed  2  or  3  hours.  It  might  be  added  that  the  onset  of 
symptoms  occurred  in  many  cases  very  soon  after  the  administration  of  the  drug — 
on  an  average  about  10  to  30  minutes  after  the  drug  was  injected.    After  smaller 


ACUTE  INTOXICATION — RABBITS.  37 

doses  were  administered  by  iujectioii  into  the  lumbar  muscles  the  appearance  of 
symptoms  was  delayed  several  hours  in  some  cawes.  The  duration  of  life  in  thtjse  14 
rabbits  varied  considerably.  Eight  of  them  died  within  1  to  20  hours;  six  survived. 
About  0.2  gram  caffein  per  kilo  may  be  regarded  as  the  minimum  fatal  dose,  while 
the  minim um  toxic  dose  is  somewhere  between  130  and  150  mg  per  kilo. 

INTRAVENOUS  INJECTION. 

These  experiments  were  carried  out  on  well-fed,  full-grown  gray  rabbits.  The  diet 
for  several  days  preceding  the  experiments  consisted  of  oats  or  carrots,  which  were  given 
ad  libitum.  The  injections  were  made  into  the  ear  veins  from  a  burette  or  by  means 
of  a  syringe,  the  temperature  of  the  caffein  solution  being  about  40°  C.  Attention 
was  also  directed  to  the  effect  of  the  rate  of  injection  and  of  the  concentration  on  the 
toxicity.  The  minimum  toxic  as  well  as  lethal  doses  were  determined  as  shown  in 
the  following  experiments. 

Series  A. 

In  these  experiments  the  rate  of  injection  was  about  1  cc  of  2  per  cent  caffein  solution 
per  minute. 
Rabbit  194.     While,  female.     Weight,  1,310  grams. 

October  19:  Injected  7.5  cc  2  per  cent  solution  caffein  (115  mg  per  kilo)  into  the  ear 
vein.    Rabbit  showed  stiffness;  paralysis  of  extremities  appeared  soon  after. ^f    Rabbit 
survived. 
Rabbit  556.    Gray,  female.     Weight,  1,635  grams. 

January  31:  2  p.  m.,  11  cc  2  per  cent  caffein  (134  mg  per  kilo)  injected  into  ear  vein, 
in  about  11  minutes;  2.10  p.  m.,  convulsions,  rabbit  remained  lying  on  its  side;  during 
the  rest  of  the  hour  it  had  convulsions  occasionally;  3.20  p.  m.,  convulsions  and  died. 
Rabbit  did  not  urinate  after  the  injection  of  caffein. 
Rabbit  657.    Gray,  female.     Weight,  1,.5S0  grams. 

January  31:  2.30  to  2.37  p.  m.,  7  cc  2  per  cent  caffein  injected  from  the  burette  at 
the  rate  of  1  cc  per  minute;  2.37  p.  m.,  flow  of  liquid  ceased,  veins  were  engorged  and 
bled  freely,  injection  was  continued  by  means  of  a  sjTinge;  2  cc  2  per  cent  caffein 
injected  in  two  minutes;  injections  discontinued  as  convulsions  appeared;  2.50  ]).  m., 
rabbit  raised  itself  but  fell  over;  3.10  p.  m.,  rabbit  assumed  normal  attitude,  walked 
about  the  floor  without  manifesting  any  signs  of  the  effects  of  caffein;  4.30  p.  m., 
walked  about,  gait  normal,  condition  seemed  to  be  good. 

February  1:  2  p.  m.,  condition  good,  appetite  good,  total  amount  of  caffein  injected, 
9  cc  2  per  cent  solution,  or  114  mg  per  kilo. 
Rabbit  558.    Gray,  female.     Weight,  1,590  grams. 

January  31:  3  p.  m.,  given  8  cc  2  per  cent  caffein  in  eight  minutes;  3.10  p.  m., 
violent  conAoilsions ;  3.20  p.  m.,  rabbit  was  stretched  out  on  his  abdomen,  extremities 
extended,  urinated;  4.30  p.  m.,  looked  normal;  was  able  to  walk  about. 

February  1:  2  p.  m.,  condition  good,  appetite  good. 
Rabbit  292.    Belgian  hare,  male.     Weight,  1,770  gram^. 

February  18:  4.26  to  4.39  p.  m.,  12.5  cc  warm  caffein  solution  (0.141  gram  per  kilo) 
injected  into  ear  vein,  convulsion  followed  when  this  quantity  was  injected,  tonic 
rigidity  of  limbs  followed  soon  after;  4.52  p.  m.,  condition  unchanged,  rabbit  on  floor, 
limbs  stretched  out,  and  lying  on  abdomen. 

Rabbit  294.    Belgian  hare,  female.     Weight,  1,350  grams.     Carrot  diet  for  about  10  days 
before  the  experiment. 

February  19:  12.20  p.  m.,  5  cc  2  per  cent  caffein  (74  mg  per  kilo)  injected  into 
ear  vein  in  five  minutes,  edema  of  the  ear,  other  ear  used,  3.5  cc  injected  in  10  min- 
utes, repeated  convulsions;  1.25  p.  m.,  rabbit  still  alive,  frequent  attacks  of  convul- 
sions; 2.30  p.  m.,  found  dead.  Total  amount  injected  in  15  minutes,  8.5  cc,  or  0.126 
gram  per  kilo. 

It  will  be  observed  in  the  preceding  experiments  that  symptoms  of  severe  intoxi- 
cation were  present  in  all  of  the  six  rabbits,  but  only  two  of  these  (Nos.  294  and  556) 
died  from  the  effects  of  caffein.     Of  those  which  survived,  three  received  doses  of 

a  Time  of  Injection  Inadvertently  omitted,  but  was  probably  not  slower  than  In  the  other  cases  of  this 
series. 


38  THE   TOXICITY   OF   CAFFEIN. 

100  to  114  mg  caffein  per  kilo,  and  another  (No.  292)  received  141  mg  of  caffein  per 
kilo.  The  death  of  rabbits  Nos.  294  and  556  may  be  regarded  therefore  as  a  case  of 
exceptionally  low  resistance  to  caffein. 

Series  B. 

Doses  of  160  to  200  mg  caffein  per  kilo  were  employed  in  these  experiments.    The 
rate  of  injection  was  1  cc  per  minute,  with  the  exception  of  Experiment  254,  in 
which  10.8  cc  2  per  cent  caffein  were  introduced  in  17  minutes  and  25  seconds. 
Rabbit  562.     Gray  female.     Weight,  1,650  grams.    Diet,  oats. 

February  1:  Injection  began  at  3  p.  m.,  injected  10  cc  in  12  minutes;  3.01  p.  m. 
to  3.09  p.  m.,  3  cc  injected,  convulsions;  3.09  p.  m.  to  3.14  p.  m.,  3  cc  injected,  fol- 
lowed by  violent  convulsions,  marked  opisthotonos;  4.30  p.  m.,  rabbit  died;  total 
quantity  injected,  16  cc. 
Rabbit  561.    Gray  female.     Weight,  1,450  grams.    Diet,  oats. 

February  1:  Injection  began  at  11.40  a.  m.;  11.48,  rabbit  struggled,  7  cc  2  per  cent 
caffein  injected;  11.50,  convulsions,  10  cc  2  per  cent  caffein  total  amount  injected; 
11.55  a.  m.,  injections  stopped;  injections  resumed  11.58,  violent  convulsions,  injec- 
tions discontinued,  total  quantity  received,  14.5  cc  2  per  cent  caffein  solution;  1.30 
p.  m.,  found  dead,  did  not  m-inate,  25  cc  urine  found  in  the  bladder. 
Rabbit  560.    Gray  male.     Weight,  1,620  grarris.    Diet,  oats. 

February  1:  Injection  began  11  a.  m.;  11.10  a.  m.,  7  cc  2  per  cent  caffein  injected, 
rabbit  struggled;  1  cc  was  injected  during  the  next  three  minutes,  rabbit  struggled 
but  there  were  no  convulsions,  injection  stopped;  resumed  at  11.15  a.  m.  and 
continued  10  minutes,  8  cc  2  per  cent  caffein  introduced  during  this  time;  total 
amount  caffein  injected,  16  cc;  reflexes  markedly  increased;  12  noon,  tetanic  con- 
vulsions off  and  on  until  2  p.  m.,  then  remained  stretched  out  on  abdomen,  extremi- 
ties extended. 

February  2:  9  a.  m.,  found  dead. 
Rabbit  559.    Gray  female.     Weight,  1,875  grams.    Diet,  oats. 

January  31:  4  p.  m.,  convulsions  after  injection  of  9  cc  2  per  cent  caffein  in  14 
minutes;  4.08  p.  m.,  convulsions  after  injection  of  7  cc  caffein  in  8  minues;  4.10  to 
4.12  p.  m.,  injected  2  cc  more,  rabbit  lying  stretched  out  on  abdomen,  extremities 
extended;  total  amount  of  caffein  injected,  18  cc  (190  mg  per  kilo). 

February  1:  2  p.  m.,  condition  good,  walked  about,  appetite  good,  passed  155  cc 
dark,  reddish-brown  urine  since  5.30  p.  m.  previous  day. 
Rabbit  279.    Gray  and  white  female.     Weight,  1,S20  grams. 

February  24:  10.09  a.  m.,  6  cc  2  per  cent  caffein  passed  rapidly  into  jugular  vein; 
10.15  a.  m.,  involuntary  twitching  of  muscles  of  legs,  but  no  other  symptoms;  10.23 
to  10.26,  3  cc  of  2  per  cent  caffein  injected;  10.27  to  10.28,  2  cc  2  per  cent  caffein 
injected,  convulsions;  10.29,  convulsions  stopped;  10.32,  convulsions;  11  a.  m.,  rab- 
bit lying  on  its  side,  anterior  extremities  paralyzed,  posterior  extremities  contracted, 
no  clonic  convulsions,  breathed  deeper  and  more  slowly  than  normal;  11.10  a.  m., 
rabbit  died,  had  no  convulsions  immediately  before  death;  amount  of  caffein  injected, 
11  cc  2  per  cent  solution,  or  0.166  gram  per  kilo. 
Rabbit  254.     Belgian  hare,  female.     Weight,  1,285  grams.     Diet,  oats. 

November  12:  1.30J  to  1.47f  p.  m.,  received  10.8  cc  2  per  cent  caffein  from  burette 
into  ear  vein,  after  injection  of  6.2  cc  dyspnoea,  6.7  cc  struggling,  convulsions;  at 
1.50^  p.  m.,  released  from  holder,  paralysis  especially  marked  in  the  anterior  extremi- 
ties; 1.50  p.  m.,  recovered,  survived;  total  amount  injected^  10.8  cc  2  per  cent 
caffein  in  17  minutes  and  25  seconds,  or  0.16  gram  caffein  per  kilo. 
Rabbit  255.    Belgian  hare,  male.     Weight,  1,105  grams.    Diet,  oats. 

November  12:  2.311  to  2.35i  p.  m.,  received  3.7  cc;  from  2.37^  to  2.46J-  p.  m.,  5  cc 
injected;  after  injection  of  6.1  cc  convulsions  followed  by  dyspnoea,  then  contin- 
uous struggling;  when  8.3  cc  were  injected  rabbit  had  another  convulsion;  2.47  p.  m., 
tonic  contraction  of  anterior  extremities;  amount  injected,  8.7  cc  (158  mg  per  kilo) 
in  15  minutes  and  35  seconds. 
Rabbit  567.    Gray  female.     Diet,  oats. 

February  6:  Injection  began  at  4.11  p.  m.;  4.18,  convulsions  after  injection  of 
5  cc  2  per  cent  caffein;  4.21,  convulsion  after  total  injection  of  8  cc;  4.24  p.  m.,  injec- 
tion resumed  and  2  cc  more  introduced;  4.28  p.  m.,  convulsions,  injected  2  cc  more; 
total  caffein  injected,  12  cc,  or  162  mg  per  kilo;  4.40  p.  m.,  rabbit  paralyzed  in  pos- 
terior extremities;  5  p.  m.,  found  dead. 


ACUTE   INTOXICATION — RABBITS.  39 

In  the  eight  experimentH  compriHinp  soricH  B  nibbit.s  Noh.  oG7,  254,  279,  and  255, 
which  may  be  dcHignuted  as  Group  II,  received  doHcs  of  lfj2,  IfJO,  IGG,  and  158  mg, 
respectively.  Nos.  5(>2,  oGl,  5(50,  and  559,  which  may  be  designated  as  Group  I, 
received  about  200  nig  caffein  per  kilo.  In  Group  II,  which  received  the  smaller 
doses,  one  (No.  254)  survived.  This  may  be  regarded  aH  exceptional,  since,  a.s  was 
shown  in  the  experiments  of  the  preceding  series,  even  smaller  doses  may  be  fatal. 
About  IGO  mg  ])or  kilo  is,  therefore,  the  smallest  surely  fatal  dose.  Thus  might  be 
regarded  aa  a  contradiction  of  the  results  obtained  for  rabbit  No.  559,  but  it  will  be 
noticed  that  in  this  Ciise  diuresis  was  very  marked.  The  results  of  experiments 
Nos.  294  and  255  are  of  interest  in  this  connection,  since  they  indicate  that  a  moderate 
difference  in  the  rate  of  injection  is  without  any  effect  on  the  toxicity  of  caffein. 
The  greater  resistance  to  caffein  of  rabbit  No.  559  is  in  all  probability  due,  therefore, 
to  increased  diuresis. 

Series  C. 

In  these  experiments  the  minimum  toxic  dose  was  determined.  The  conditions 
were  the  same  as  in  the  experiments  of  the  other  series. 

Rabbit  29S.    Belgian  hare,  female.     Weight,  1,610  grams.    Diet,  oats. 

February  IS:  3.40  to  3.43  p.  m.,  4  cc  2  per  cent  warm  caffein  solution  injected  into 
ear  vein,  convulsions  when  3  cc  were  injected,  repeated  attacks;  4  p.  m.,  raised  itself 
on  legs,  but  fell  over  immediately  and  lay  stretched  on  abdomen. 

February  19:  9  a.  m.,  rabbit  looked  normal,  apparently  recovered. 
Rabbit  227.     White  male.     Weight,  2,320  grams. 

October  26:  3.29}  to  3.37^  p.  m.,  injected  into  ear  from  burette  G.7  cc  2  per  cent 
caffein,  no  symptoms;  experiment  discontinued;  survived. 
Rabbit  563.     Gray  female.     Weight,  1,650  grams.     Diet,  oats. 

February  G:  Injection  began  at  1.02  p.  m.,  injected  3.5  cc  2  per  cent  caffein  (42  mg 
per  kilo)  in  four  minutes,  O.G  cc  more  Avithin  the  next  two  and  one-half  minutes,  total 
amount  injected  4.1  cc;  1.10  p.  m.,  hypersensitive,  some  disturbance  of  muscular 
coordination;  restlessness;  1.35.  p  m.,  reflexes  decreased,  urinated  and  walked  about, 
gait  normal.  Under  observation  for  several  days;  no  symptoms  noted. 
Rabbit  564.     Gray  female.     Weight,  1,515  grams. 

February  6:  Injection  began  at  1.26  p.  m.,  3.5  cc  2  per  cent  caffein  (46  mg  per  kilo) 
injected  at  the  rate  of  1  cc  per  minute;  1.30  p.  m.,  reflexes  increa.sed;  1.34  p.  m., 
marked  paresis  of  the  extremities,  rabbit  stretched  out  on  abdomen,  legs  abducted 
and  partly  extended,  able  to  hop  about  but  gait  disturbed,  no  untoward  symptoms 
noticed,  under  observation  for  several  days  after  experiment. 
Rabbit  565.     Gray  female.     Weight,  1,. 545  grains.     Diet,  oats. 

February  G:  Started  to  inject  at  3.40  p.  m.,  received  2.5  cc  2  per  cent  cafTein  intra- 
venously in  two  minutes  or  32  mg  per  kilo,  under  observation  all  afternoon,  no 
symptoms. 

Rabbit  566.    Gray  female.     Weight,  1,900  gram^.    Diet  oats. 

February  G:  Injection  began  at  3.05  p.  m.,  received  3  cc  2  per  cent  caffein  intra- 
venously in  three  minutes  or  31  mg  per  kilo,  no  symptoms  observed. 

These  experiments  show  that  a  dose  of  about  50  mg  per  kilo  when  injected  intra- 
venously produces  mild  symptoms,  such  as  increased  reflexes.  In  the  four  experi- 
ments with  this  amount  of  caffein  these  effects  were  observed  in  each  case.  In  the 
experiments  in  which  smaller  quantities,  30  mg  per  kilo,  were  given  intravenously 
there  was  no  manifestation  of  symptoms.  A  dose  not  over  50  mg  per  kilo  may,  there- 
fore, be  regarded  as  the  minimum  toxic  dose  when  injected  intravenously  under  the 
conditions  stated . 

Series  D. 

A  0.5  per  cent  caffein  solution  was  used  in  these  experiments  in  order  to  test  the 
effect  of  concentration  on  its  toxicity;  the  rate  of  injection  was  1  cc  per  minute. 
Rabbit  569.    Gray  male.     Weight,  1,475  grams.    Diet,  oats. 

February  6:  11.50  a.  m.  to  12.01  p.  ni.,  injected  10  cc  0.5  per  cent  caffein;  12.03 
to  12.12  p    m.,  injected  10  cc  of  0.5  per  cent  caffein;  12.13  to  12.26  p.  m.,  injected 


40  THE   TOXICITY   OF   CAFFEIN". 

10  cc  of  0.5  per  cent  caffein,  total  amount  injected,  30  cc;  12.20,  passed  35  cc  of  urine; 
12.30,  increased  reflexes,  but  no  convulsions;  4  p.  m.,  reflexes  increased. 

February  11:  Alive,  condition  good. 
Rabbit  574-     Gray  female.     Weight,  1,555  grams.    Diet,  oats. 

February  8:  10.25  to  10.33  a.  m.,  injected  4  cc  of  0.5  per  cent  caffein  in  salt  solution, 
injection  discontinued  for  five  minutes;  10.38  to  11.10,  injected  30  cc,  total  amount 
of  caffein  solution  received,  34  cc;  11.55  a.  m.,  very  sensitive;  reflexes  markedly 
increased. 

I     February  9:  Alive,  condition  good. 
Rabbit  571.     Gray  female.     Weight,  1,530  grams.     Diet,  oats. 

February  7:  Injection  3.18  to  3.50  p.  m.,  received  30  cc  in  32  minutes,  not  hyper- 
sensitive; 3.55,  restlessness  and  weakness  of  extremities;  4.10  p.  m.,  control  of  ante- 
rior extremities  impaired,  distinctly  paretic  but  tried  to  walk  about,  died  the  same 
afternoon. 
Rabbit  568.    Gray  male.     Weight,  1,605  grams.    Diet,  oats. 

February  7:  Injection  10.53  to  11.01  a.  m.,  injected  10  cc  0.5  per  cent  caffein;  11.03, 
injection  resumed  after  two  minutes  interval;  11.14,  received  10  cc  0.5  per  cent 
caffein  intravenously  in  11  minutes;  11.16,  injection  resumed;  11.35,  received  12  cc 
0.5  per  cent  caffein,  total  amount  of  caffein  solution  received,  32  cc;  12.30  p.  m., 
urinated  14  cc  of  bloody  urine;  12.55  p.  m.,  convulsions  and  death  a  few  minutes  later. 
Autopsy  showed  congestion  of  viscera,  but  no  other  lesions. 
Rabbit  570.     Gray  female.     Weight,  1,225  grams.     Diet,  oats. 

February  7:  2.06  to  2.35  p.  m.,  injected  24.5  cc  0.5  per  cent  caffein,  reflexes  increased 
but  no  convulsions,  paresis  especially  marked  in  the  anterior  extremities;  3  p.  m., 
passed  xuine  which  was  normal  in  appearance,  reflexes  not  increased  but  rabbit  was 
weak. 

February  9:  Found  dead.  Autopsy:  Liver,  spleen,  and  kidneys  congested;  large 
intestines  hemorrhagic;  omentum  congested  and  showed  the  presence  of  small  caseous 
nodules;  liver  showed  adhesion  to  diaphragm;  viscera  presented  the  appearance  of 
intraabdominal  infection. 

I  Of  the  five  rabbits  of  this  series  three  died  as  a  result  of  the  administration  of  caffein. 
The  other  two  which  survived  showed  mild  symptoms  only,  such  as  increased  reflexes, 
but  no  evidence  of  severe  poisoning  such  as  was  observed  after  the  injection  of  the 
same  doses  of  caffein  in  series  A  when  a  2  per  cent  solution  of  caffein  was  injected. 
Convulsions  were  noticed  in  one  case  only  (No.  568);  paresis  in  two  cases  (Nos.  570 
and  571).  The  nervous  symptoms  even  in  this  group,  therefore,  were  much  milder 
than  in  series  A.  The  percentage  of  death,  however,  was  greater  than  in  series  A,  in 
which  the  concentration  of  caffein  was  four  times  as  great.  It  is  quite  probable  that 
the  strain  on  the  heart  due  to  the  sudden  increase  in  volume  of  the  blood  and  its  dilu- 
tion might  be  an  important  factor  in  increasing  the  toxicity  of  caffein.  It  is  conceiv- 
able that  doses  just  sufficiently  large  to  depress  the  normal  heart  may  cause  paralysis 
of  an  already  overstrained  organ. 

Series  E. 

In  the  two  experiments  of  this  series  the  rate  of  injection  as  a  possible  factor  influ- 
encing the  toxicity  of  caffein  was  tested.  A  2  per  cent  caffein  solution  was  injected 
at  the  rate  of  1  cc  in  two  and  one-half  to  three  minutes. 

Rabbit  572.    Gray  male.     Weight,  1,770  grams.     Diet,  oats. 

February  8:  Injection  began  at  3  p.  m.,  discontinued  at  3.37  p.  m.,  and  resumed  at 
3.38  p.  m. ;  rabbitwas  restless;  injection  finished  at  3.52  p.  m.  Total  quantity  received, 
17.4  cc  2  i^er  cent  caffein  intravenously  in  52  minutes;  struggled  intermittently  during 
the  injection;  anterior  legs  paralyzed. 

February  9:  Found  dead. 
Rabbit  57.3.     Gray  male.     Weight,  1,810  grams.     Diet,  oats. 

Februarys:  Started  to  inject  at  1.35  and  discontinued  at  2.27  p.  m.;  received  18  cc 
2  per  cent  caffein  intravenously  in  52  minutes;  reflexes  markedly  increased  soon 
after;  2.45,  passed  bloody  urine;  4.30  p.  m.  reflexes  increased;  no  other  symptoms. 

February  9:  9  a.  m.,  found  dead. 

It  will  be  observed  that  some  retardation  of  the  onset  of  symptoms  was  caused  by 
slower  injection,  but  the  final  result  was  the  same  as  when  liie  injections  were  made 


ACUTE  INTOXICATION — RABBITS. 


41 


more  rapidly.     It  is  ciiiito  probable,  therefore,  that  a  much  slower  rate  of  injection 
may  lessen  considerably  the  toxicity  of  caffein. 

From  the  re.'^ults  of  the  experiraenta  by  intravenous  injection  summarized  in  the 
table,  it  appears  that  tlie  niiuinuim  toxic  dose  for  rabbits  of  a  2  per  cent  caffein  solu- 
tion, injected  at  the  rate  of  1  cc  per  minute,  is  about  50  mg  per  kilo.  Twice  the  dose 
induces  severe  symptoms  and  may  be  fatal;  1(50  mg  per  kilo  are  surely  fatal.  If  the 
rate  of  injection  is  diminished,  the  toxit-ity  of  caffein  is  lessened,  but  this  effect  is 
not  marked  unless  the  injections  are  very  slow.  Dilution  of  the  caffein  solution  sup- 
presses to  some  extent  the  nervous  symptoms,  but  the  toxicity,  on  the  contrary,  eeema 
to  be  increased. 

Table  5. — Intravenous  injecticms. 

SERIES  X. 


No. 

Weipht. 

Caftcia 
per 
kilo. 

Symptoms. 

Duration  of  life. 

Diet. 

Remarks. 

1f)4 

Orams. 
1,310 
1,635 
1,580 
1,590 
1,770 
1,350 

Mg. 
114 
134 
114 
100 
141 
126 

Present... 
10  minutes 
Present... 
...do 

Survived 

Oats 

...do 

Mfi 

20  minutes 

Gray  female. 

f\M 

Survived 

..do 

558 

do 

.do..   .. 

Do. 

■X)-> 

...do 

do 

...do 

Do. 

1<»4 

...do 

10  minutes 

Carrots 

Do. 

SERIES  B,  GROUP  I. 


w 

1.650 
1,450 
1,620 
1,875 

200 
200 
200 
190 

1 J  hours 

Oats 

.do 

Gray  female. 

5til 

do 

5ti0 

Present... 
...do 

Less  than  24  hours 

.do  . 

Do. 

."vSq 

Survived 

...do 

Do. 

SERIES  B,  GROUP  II. 


?7<» 

1,320 
1,285 

166 
160 
162 
158 

1  hour 

Gray  and  white  female. 
Grayfemale. 

?54 

Survived 

Oats 

.567 

?'>.5 

Died 

SERIES  C. 


M? 

1,610 
2,320 
1,650 
1,515 
1,545 
1,900 

500 
570 
500 
460 
320 
310 

Present. . . 
None 

Survived 

Oats 

Gray  female. 

??7 

do 

56.{ 

Present. . . 
...do 

do 

.do 

Grayfemale. 

.')fi4 

do 

.S65 

None 

do 

.do  .   . 

Do. 

566 

...do 

do 

...do 

Do. 

SERIES  D. 


<m 

1,475 
1,5.55 
1,530 
1,605 
1,225 

100 
112 
100 
100 
100 

Present... 
...do 

Survived 

Oats 

do 

Gray  male. 
Grayfemale. 

.574 

..   ..do 

.571 

...do 

About  2  hours 

...do 

.56,S 

20  minutes 

.do 

.570 

.  .do 

"Do 

SERIES  E. 


.572 

1,770 
1,810 

200 
200 

Present.. 

.    About  24  hours 

Oats 

.do     . 

fiV.I 

do 

i                 ■ 

42  THE   TOXICITY   OF   CAFFEIN". 

SUMMARY. 

The  results  of  the  experiments  on  rabbits  show  considerable  variation  in  the  toxicity 
of  the  single  dose.  Individuals  differed  so  widely  in  their  resistance  to  this  drug 
that  the  same  experiments  had  to  be  repeated  many  times  with  each  method  of  ad- 
ministration before  satisfactoiy  conclusions  could  be  drawn.  This  is  strikingly 
illustrated  in  the  experiments  by  intravenous  injection  in  which  a  dose  of  nearly  0.2 
gram  per  kilo  was  not  fatal.  Similar  instances  of  exceptional  resistance  or  of  sensi- 
tiveness to  caffein  were  observed  when  it  was  given  in  other  ways.  A  comparison 
of  the  toxicity  of  caffein  administered  by  different  methods  in  this  investigation 
shows  well-marked  differences  in  its  activity,  although  they  are  not  quite  so  striking 
as  similar  experiments  with  other  alkaloids  reported  by  several  observers.  The  tox- 
icity of  caffein  in  these  experiments  on  the  rabbit  indicates  that  it  is  greatest  when 
given  by  vein  and  least  when  given  by  mouth.  The  ratio  of  the  minimum  toxic 
doses  by  these  two  methods  of  introduction  of  caffein  was  about  7.1;  the  relation  of 
the  miaimum  fatal  dose  was  about  3.1.  The  toxicity  when  given  subcutaneously  is 
about  15  to  20  per  cant  greater  than  when  given  by  mouth.  The  difference  between 
the  intramuscular  and  subcutaneous  injection  is  even  more  marked.  The  toxicity 
of  caffein  when  injected  into  the  muscles  is  about  midway  between  that  adminis- 
tered by  the  subcutaneous  and  intraperitoneal  routes,  and  is  about  half  that  injected 
intravenously.  Meltzer  and  Auer,  **  who  experimented  with  a  number  of  drugs 
found  that  the  intramuscular  method  of  administration  is  as  effective  as  the  intravenous, 
fluorescin  formiag  the  only  exception  according  to  their  observations.  In  the  experi- 
ments of  Sollman  and  Brown  *^  with  ergot,  the  effect  was  quite  different  from  those 
obtained  by  Meltzer  and  Auer  ^^  with  the  drugs  they  used.  It  is  quite  possible  that 
the  result  obtained  with  ergot  is  merely  illustrative  of  a  difference  in  the  behavior  of 
various  substances  in  this  regard.  This  appears  probable  on  account  of  the  difference 
in  the  rate  of  absorption  for  various  substances.  Thus,  according  to  Achard,  Gaillard, 
and  Ribot  (Compt.  rend.  Soc.  biol.,  1907,  62:  90),  absorption  from  the  peritoneal 
cavity  varies  with  the  concentration  of  the  solution  and  the  size  of  the  molecule.  The 
smaller  the  molecule  and  the  greater  the  concentration  the  more  rapid  the  absorp- 
tion. That  the  rate  of  absorption  from  the  intramuscular  tissues  is  unequal  and 
varies  for  different  substances  appears  from  the  experiments  of  Meltzer  and  Auer.  ^^ 
The  difference  was  very  striking  between  intramuscular  and  subcutaneous  adminis- 
tration of  curara  or  adrenalin;  the  results  were  somewhat  different  with  morphin  and 
with  fluorescin.  As  shown  in  their  protocols,  the  onset  of  the  symptoms  after  the 
intramuscular  injection  of  morphin  was  sooner  than  after  subcutaneous  injection, 
but  in  time  the  difference  diminishes  and  disappears  altogether.  The  absorption  of 
fluorescin  is  much  faster  when  the  intramuscular  path  is  used  than  when  given  sub- 
cutaneously, but  the  writers  state  that  the  rate  falls  far  behind  that  of  the  intravenous 
administration.  The  difference  in  toxicity  we  observed  between  feeding  by  mouth 
and  subcutaneous  injection,  although  distinct,  was  not  very  great.  It  was  much 
less  than  Maurel  ^^  obtained  with  the  hydrobromid  of  caffein  in  the  rabbit.  Whether 
this  difference  between  his  results  and  ours  is  due  to  the  use  of  the  pure  alkaloid  in  '; 
our  experiments  and  the  hydrobromid  employed  by  Maurel  can  not  be  stated  at  < 
present  with  any  degree  of  accuracy.  It  is  hoped  that  the  work  in  progress  in  the 
laboratory  will  throw  some  light  on  the  subject  in  the  near  future.  But  Maurel's  "" 
experiments  show  that  various  substances  behave  differently  in  this  regard.  Thus 
the  toxicity  of  strychnin,  he  states,  is  three  times  as  great  when  given  subcutane- 
ously as  when  given  by  mouth  and  six  times  that  of  the  minimum  fatal  dose  by  vein. 
It  may  be  remarked,  however,  that  examination  of  his  data  shows  that  his  doses  are 
much  too  large  for  the  rabbit.  In  experiments  with  other  drugs  little  or  no  difference 
between  the  two  modes  of  administration  was  noticed.  Thus,  digitalin  was  but 
slightly  more  active  when  given  subcutaneously  than  by  mouth,  while  the  toxicity 
of  emetin  hydrochlorid  was  just  the  same,  whichever  one  of  these  methods  of  Intro- 


ACUTE   INTOXICATiaN GUINEA  PIGS.  43 

ducing  the  subatance  was  used.  Differences  in  the  toxicity  of  substances  have  also 
been  observed  betweeu  subcutaneous  and  iutruvenijurf  modes  of  administration, 
but  here,  too,  the  differtjucvs  for  vatious  substances  wore  unequal. 

EXPERIMENTS  ON  GUINEA  PIGS. 

The  toxicity  of  caffein  was  studied  in  a  large  number  of  individuals.  The  experi- 
ments were  conducted  on  fuU-j^rown  animals  and  were  carried  out  at  different  seasons 
of  the  year  in  a  variety  of  ways.  Special  attention  was  given  to  di-it  aa  a  poasible 
factor  influencing  resistance  to  caffein,  and  the  effect  of  different  modes  of  adminis- 
tration on  toxicity.  Some  animals  were  therefore  fed  oats,  some  carrots,  others  re- 
ceived both  hay  and  oats.  Caffein  was  introduced  subcutaneously,  intraperitoneally, 
and  by  mouth. 

SUBCUTANEOUS  INJECTION. 

Series  A. 

Preliminary  experiraentd  carried  out  on  three  guinea  pigs,  which  received  360, 
300,  and  290  mg  of  caffein  per  kilo  subcutaneously  have  shown  that  such  doses  were 
rapidly  fatal.  Two  of  the  animals  were  seized  with  convulsions  half  an  hour  after 
the  introduction  of  caffein  and  died  during  the  attack.  The  other  had  tetanus  two 
minutes  after  the  injection  of  caffein.  Repeated  attacks  followed,  which  terminated 
in  the  death  of  the  animal  two  and  a  half  hours  later.  The  fatal  and  toxic  doses  must 
therefore  be  considerably  under  0.3  gram  of  caffein  per  kilo  when  introduced  by  this 
path  and  smaller  doses  were  therefore  injected.  The  results  are  shown  in  the  experi- 
ments of  the  next  series. 

Series  B. 

Experiments  with  2  decigrams  per  kilo  constituted  this  series. 
Guinea  pig  20.     Female.     Weight,  497  grams.    Diet,  oats. 

April  2:  5  cc  2  per  cent  caffein  injected  subcutaneously  at  11.30  a.  m.;  1.50  p.  m., 
epasm  of  short  duration.     Died  at  3  p.  m.,  three  and  one-naif  hours  after  injection. 
Guinea  pig  S8.    Brovm  male.     Weight,  570  gram^.    Diet,  carrots  and  oats  week  previous 
to  injection. 

February  11:  3.50  p.  m.,  6  cc  2  per  cent  caffein  injected  subcutaneously  in  back 
(210  mg  per  kilo);  4.15,  reflexes  increased,  had  convulsion  of  short  duration  when 
disturbed;  4.45  p.  m.,  on  handling,  repeated  convulsion  and  paralysis;  5  p.  m.,  guinea 
pig  l>"ing  on  his  side,  respiration  difficult  and  labored. 

February  11:  5.05  p.  m.,  guinea  pig  found  dead,  2  hours  and  15  minutes  after 
injection. 

Guinea  pig  37.     Male.     Weight,  820  grains.    Diet,  carrots  and  oats  during  week  pre- 
ceding the  injection  ofcafein. 

February  11:  3.35  p.  m.,  8.5  cc  2  per  cent  caffein  injected  subcutaneously  in  the 
back;  5  p.  m.,  pig  very  sensitive,  anterior  extremities  paralyzed  when  handled,  fre- 
quent spasms  of  posterior  extremities,  no  symptoms  noticed  before  5  p.  m.,  although 
watched  all  the  time;  5.05  p.  m.,  guinea  pig  on  his  legs  and  looked  normal.  No  attack 
on  handling. 

February  12:  9  a.  m.,  found  dead;  died  within  18  hours. 
Guinea  pig  l.L     Female.     Weight,  61S  grams.     Diet,  oats. 

March  29:  2.45,  6  cc  2  per  cent  caffein  injected  subcutaneously  (0.194  grams  per 
kilo). 

March  30:  Died  at  4  p.  m.,  25  hours  after  injection. 
Guinea  pig  36.     Male.     Weight,  850  grams.     Fed  oafs  and  carrots  for  one  week  previous 
to  injection. 

February  11:  3.30  p.  m.,  8.5  cc  2  per  cent  caffein  injected  subcutaneously  into 
back;  5  p.  m.,  somewhat  more  sensitive  than  normal,  no  other  symptoms,  no  effect 
on  handling;  5.05  p.  m.,  no  symptoms. 

February  12:  9  a.  m.,  found  dead,  about  18  hours  after  injection. 

The  results  of  these  experiments,  as  observed  in  five  guinea  pigs,  indicate  that 
two  decigrams  of  caffein  per  kilo  of  animal  produce  svTmptoms  within  a  half  to  about 
two  and  a  quarter  hours  after  injection.    Death  followed  iu  two  guinea  pigs  70  minutes 


44  THE   TOXICITY   OP   CAFFEIN. 

to  1  hour  after  the  first  manifestations  of  symptoms.  Two  others  died  during  the 
night,  while  one  lived  25  hours  after  the  injection  of  caffein.  Even  2  decigrams 
caffein  per  kilo  weight  might  therefore  be  fatal  to  the  guinea  pig.  Experiments 
carried  out  later  have  shown,  however,  that  the  resistance  to  caffein  is  appreciably 
greater  in  some  guinea  pigs.  This  is  indicated  by  the  following  experiments,  in  which 
doses  of  0.2  to  0.24  gram  caffein  per  kilo  were  administered  by  the  same  path. 

Series  C. 

Guinea  pig  66.     Yellow  and  dark  brown  male.     Weight,  510  grams.    Diet,  oats. 

October  4:  5  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  subcutaneously  in 
the  back  at  3  p.  m.;  5  p.  m.,  no  symptoms. 

October  5:  9  a.  m.,  alive;  condition  good. 

October  9:  Found  dead.  Autopsy:  Congestion  of  liver,  kidney,  and  small  intestine. 
Guinea  pig  65.     White  and  black  male.     Weight,  510  grams.    Diet,  oats. 

October  4:  5  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  subcutaneously  in 
the  back  at  3  p.  m.;  5  p.  m.,  no  symptoms. 

October  5:9  a.  m.,  condition  good. 
Guinea  pig  60.     White  and  gray  female.     Weight,  320  grams.    Diet,  oats. 

October  3:  2.25  p.  m.,  3.5  cc  2  per  cent  caffein  ((0.219  gram  per  kilo)  injected  sub- 
cutaneously in  the  back;  3.40  p.  m.,  convulsion  with  recovery;  3.50  p.  m.,  frequent 
spasms  with  paralysis,  especially  of  anterior  extremities;  5.30  p.  m.,  tetanus  when 
removed  from  cage  and  put  on  floor. 

October  4:  8.50  a.  m.,  found  dead.    Autopsy:  Congestion  of  small  intestines,  limgs, 
liver. 
Guinea  pig  57.     White  and  gray  female.     Weight,  350  grams.    Diet,  oats. 

October  3:  2.15  p.  m.,  3.5  cc  2  per  cent  caffein  injected  subcutaneously  in  the  back 
(0.2  gram  per  kilo);  3.40  p.  m.,  convulsions  with  recovery;  5.30  p.  m.,  no  marked 
symptoms. 

October  4:  8.50  a.  m.,  alive,  active. 

October  6:  Found  dead  at  9  a.  m.    Autopsy:  Congestion  of  lungs  and  liver;  kidneys 
petechiated;  severe  gastro-enteritis. 
Guinea  pig  68.     Yellow  male.     Weight,  785  grams.    Diet,  oats. 

October  6:  11.35  a.  m.,  7.8  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  subcu- 
taneously; 12  noon,  reflexes  increased  markedly;  4.20  p.  m.,  reflexes  the  same  as  at 
12  noon. 

October  7:  9  a.  m.,  dead.    Autopsy:  Limgs  congested;  liver  congested  and  fatty; 
spleen  congested,  kidney  showed  hemorrhagic  spots;  gastric  mucosa  necrotic;  small 
portion  of  small  intestine  inflamed. 
Guinea  pig  69.     White  male.     Weight,  585  grams.    Diet,  oats. 

October  6:  11.40  a.  m.,  5.8  cc  2  per  cent  caffein  injected  subcutaneously;  12  noon, 
reflexes  increased,  but  not  as  much  as  in  No.  68;  4.20  p.  m.,  guinea  pig  hypersensitive, 
reflexes  increased  more  than  at  12  noon. 

October  7:9  a.  m.,  alive. 

October  15:  9  a.  m.,  found  dead. 
Guinea  pig  61.    Brown  and  black  female.     Weight,  330  grams.    Diet,  oats. 

October  3 :  4  p.  m.^  4  cc  2  per  cent  caffein  (240  mg  per  kilo)  injected  subcutaneously; 
5.30  p.  m.,  reflexes  increased;  runs,  but  drags  posterior  extremities. 

October  4:  8.50  a.  m.,  found  dead. 
Guinea  pig  62.     White,  yellow,  and  black  female.     Weight,  335  grams.    Diet,  oats. 

October  3:  4.05  p.  m.,  4  cc  2  per  cent  caffein  (238  mg  per  kilo)  injected  subcu- 
taneously in  the  back;  5  p.  m.,  convulsions;  5.20  p.  m.,  convulsions,  alternating  with 
paralysis  of  anterior  and  posterior  extremities. 

October  4:  8.50  a.  m.,  found  dead. 
Guinea  pig  10.     White  and  brown  male.     Weight,  545  grams.    Diet,  oats. 

October  7:  3  p.  m.,  6.5  cc  2  per  cent  caffein  (238  mg  per  kilo)  aqueous  solution 
injected  subcutaneously;  3.50  p.  m.,  reflexes  increased. 

October  9:  9  a.  m.,  found  dead. 
Guinea  pig  71.    Br ovm  and  white  male.     Weight,  540  grams.    Diet,  oats. 

October  7:  3  p.  m.,  6.5  cc  2  per  cent  caffein  solution  (0.24  gram  per  kilo)  injected 
subcutaneously;  3.45  p.  m.,  reflexes  increased,  tetanus. 

October  9:  9  a.  ui.,  found  dead. 


ACUTE   INTOXICATION — GUINEA  PIGS.  45 

Guinea  pig  72.     Brown  and  white  male.     Weipht,  .560  grams.    Diet,  oats. 

October  7:  3  p.  m.,  6.5  cc  2  per  cent  caffein  (0.232  gram  per  kilo)  aoueous  solution 
administered  by  subcutaneous  injection;  3.35  p.  m.,  reflexen  increa.><eu. 

October  10:  found  dead.     Autopsy:  Nos.  70,  71,  72  showed  congestion  of  organs. 

The  reaction  to  caffein  in  the  e.xperimcnta  of  this  series  (C)  showed  considerable 
variation.  Tiie  appearance  of  symptoms,  as  well  as  the  final  outcome  of  the  experi- 
ments, differed  markedly  in  a  number  of  cases,  notwithstanding  the  fact  that  tho 
conditions  were  the  same;  thus  the  administration  of  0.2  gram  per  kilo  to  guinea 
pigs,  all  of  which  received  the  same  diet,  induced  no  symptoms  in  two  of  the  animals 
(Nos.  66  and  65),  while  marked  symptoms  were  observed  in  the  other  four;  in  two 
of  these  tho  symptoms  appeared  in  one  hour  and  a  quarter  after  injection,  and  in  two 
others  (No.-<.  68  and  69),  mild  symptoms  only  appeared  in  20  or  25  minutes.  Tlie 
last  two  were  under  observation  for  4  hours  longer,  but  there  was  no  visible  change 
in  their  condition.  The  duration  of  life  in  all  of  these  guinea  pigs,  as  indicated  in 
the  table,  likewise  varied.  Two  (Nos.  60  and  68)  died  during  the  night  after  they 
received  caffein,  one  survived  (No.  65),  and  three  others  (Nos.  57,  66,  and  69)  lived 
2J,  5,  and  9  days,  respectively.  Experiments  with  larger  doses  likewise  showed 
differences  in  the  behavior  of  these  animals  toward  caffein,  but  they  were  not  quite 
80  marked.  As  shown  in  the  table,  symptoms  appeared  in  from  35  minutes  to  1 .5  hours 
after  injection.  The  duration  of  life  was  less  than  1  day  in  two  pigs,  about  twice  as 
long  in  two  others,  and  in  one  case  between  2  and  3  days. 

A  comparison  made  with  results  obtained  in  the  preceding  series  shows  a  striking 
difference  in  the  resistance  to  caffein.  As  2  decigrams  per  kilo  proved  more  rapidly 
fatal  to  the  guinea  pig  than  the  larger  doses  employed  in  the  later  experiments,  this 
difference  in  the  resistance  to  caffein  may  be  due  to  several  factors.  As  pointed  out 
in  the  experiments  on  rabbits,  age  might  be  an  important  factor  influencing  the 
toxicity  of  caffein.  Unfortunately,  no  accurate  data  were  available  on  the  age  of  the 
guinea  pigs,  but  they  were  all  apparently  full  grown,  although  they  differed  in  weight 
considerably.  The  difference  in  their  ages  was  in  all  probability  not  ver>'  great. 
Moreover,  it  will  be  observed  that  the  resistance  in  series  B  and  C  differed  in  animals 
of  approximately  the  same  weight.  This  is  evident  on  comparing  experiments  Nos. 
20,  38,  and  13  of  series  B  with  Nos.  65,  66,  and  69  of  the  next  series.  Again,  further 
inspection  and  analysis  of  these  tables  show  no  difference  in  the  toxicity,  although 
there  may  be  considerable  difference  in  the  weight,  from  which  it  may  be  concluded 
that  the  animals  were  of  about  the  same  age  or  that  this  plays  no  part  in  the  resistance 
to  caffein  in  the  guinea  pig. 

Diet  is  another  factor  which  should  be  taken  into  consideration  in  this  connection. 
The  recent  work  of  Ilunt^'  indicates  that  this  may  influence  the  resistance  of  animals 
to  some  poisons.  Our  experiments,  however,  fail  to  show  any  difference  in  the  toxicity 
of  the  caffein  in  guinea  pigs,  whether  fed  oats,  carrots,  or  both,  for  different  results  were 
obtained  on  the  same  diet,  and  there  seemed  to  be  little  or  no  difference  in  the  toxicity 
of  caffein  when  the  diet  was  different.  Other  explanations  suggest  themselves  to 
account  for  the  results  obtained.  Seasonal  changes  have  been  assigned  by  a  number 
of  investigators  as  a  cause  of  variation  in  the  resistance  to  drugs.  According  to  Focke,-* 
frogs  are  more  susceptible  to  digitalis  in  the  spring  than  in  the  summer,  while  Mosch- 
kowitsch  **  and  Edmunds  -'  reported  the  very  opposite  results.  Schmiedeberg's  ^ 
obsers-ations  on  strophantin  in  frogs  were  in  harmony  with  those  of  Edmimds  -^  and 
Moschkowitsch."^  Similar  results  were  reported  with  guinea  pigs.  Harrington's  ^* 
experiments  indicate  that  stimulation  of  the  vagus  is  less  effective  from  October  to 
January  than  from  February  to  April,  when  they  are  also  much  more  susceptible  to 
operative  procedure.  Hunt  found  that  the  resistance  of  guinea  pigs  to  aceto  nitril  is 
about  twice  as  great  in  the  summer  months  as  it  is  in  January  and  February. 

Race  might  also  be  thought  of  as  an  important  factor  in  this  connection.  Since  the 
guinea  pigs  used  at  different  seasons  of  the  year  were  of  several  varieties,  there  is  no 


46  THE  TOXICITY   OF   CAFFEIN. 

reason  to  suppose,  however,  that  the  varieties  experimented  upon  in  the  summer 
were  more  resistant  than  those  used  in  the  winter  and  spring.  It  is  highly  probable, 
therefore,  that  the  greater  resistance  to  caffein  of  the  guinea  pigs  of  series  C  than  those 
of  series  B  was  due  to  seasonal  variation. 

Doses  of  0.20  to  0.24  gram  caffein  per  kilo  weight,  therefore,  may  be  regarded  as  the 
minimum  fatal  dose  for  the  guinea  pig,  depending  upon  the  season.  Since  0.2  gram 
per  kilo  proved  to  be  rapidly  fatal  in  series  B,  this  quantity  was  perhaps  not  the 
minimum  fatal  dose  for  the  guinea  pig  at  the  season  during  which  the  experiments 
were  made.  Additional  tests  with  smaller  doses  were  therefore  carried  out  during 
February  and  March.    The  results  are  shown  in  series  D. 

Series  D. 

Guinea  pig  49.     Male.     Weight,  510  grams.    Diet,  oats  Jor  1  month  previous  to  experi- 
ment. 

March  17:  3  p.  m.,  4  cc  2  per  cent  caffein  (0.16  gram  per  kilo)  were  injected  sub- 
cutaneously;  4.40  p.  m.,  reflexes  increased;  5.40  p.  m.,  no  symptoms. 

March  IS:  9  a.  m.,  found  dead,  died  in  less  than  18  hom-s.  Autopsy:  Hemorrhage 
into  abdominal  cavity;  liver  and  spleen  unduly  congested;  intestines  injected; 
hemorrhagic  area  at  point  of  injection. 

Guinea  pig  40.     Male.     Weight,  630  grams.    Diet,  oats  and  carrots  one  week  previous  to 
injection. 

February  12:  11  a.  m.,  5  cc  2  per  cent  caffein  (0.158  gram  per  kilo)  injected  subcu- 
taneously  into  back. 

February  13:  1  p.  m.,  still  alive. 

February  14:  9  a.  m.,  found  dead. 
Guinea  pig  45.    Female.     Weight,  435  gram^.    Diet,  oats  for  about  one  mxjnth  previous  to 
injection. 

March  17:  3  p.  m.,  3.5  cc  of  2  per  cent  caffein  injected  subcutaneously  in  the  back 
(0.160  gram  per  kilo);  4.35  p.  m.,  no  symptoms;  5.40  p  m.,  no  symptoms. 
Guinea  pig  39.     Male.     Weight,  820  grams.    Diet,  oats  and  carrots. 

February  12:  11  a.  m.,  6  cc  (0.15  gram  per  kilo)  2  per  cent  caffein  injected  subcu- 
taneously in  back. 

February  14:  9  a.  m.,  alive;  seemed  to  be  in  good  condition;  found  dead  at  1  p.  m. 
Guinea  pig  41.     Weight,  660  grams.    Diet,  oats  and  carrots  one  vjeek  previous  to  injection- 

February  12:  11  a.  m.,  5  cc  (0.15  gram  per  kilo)  2  per  cent  caffein  injected  subcu" 
taneously. 

February  14:  2  p.  m.,  pig  alive;  apparently  normal. 

February  18:  Guinea  pig  still  alive  and  apparently  in  good  condition. 
Guinea  pig  46.    Female.     Weight,  470  grants.    Diet,  oats  about  one  month  previous  to 
experiment. 

March  17 :  3.15  p.  m.,  4  cc  (0.170  gram  per  kilo)  2  per  cent  caffein  injected  into  back 
subcutaneously;  4.35  p.  m.,  reflexes  increased,  tremors  on  handling  marked;  5.40  p. 
m.,  no  change,  symptoms  about  as  before. 

March  18:  2.30  p.  m.,  no  symptoms. 

The  experiments  of  this  series  (D)  likewise  showed  a  considerable  difference  in  the 
resistance  of  the  individual  guinea  pigs.  Nos.  41,  45,  and  46  survived;  the  rest  of 
the  pigs  died  within  18  hours  to  2  days  after  the  administration  of  caffein.  Since  an 
autopsy  was  held  on  one  only,  it  is  impossible  to  assign  a  cause  for  the  variation  in  the 
toxicity  of  caffein  in  these  guinea  pigs,  as  the  diet  and  the  other  conditions  under 
which  the  experiments  were  conducted  were  the  same.  It  was  found  in  the  experi- 
ments on  cats  and  rabbits  that  the  presence  of  morbid  processes  tends  to  increase  the 
toxicity  of  caffein.  The  observations  of  Ophiils'^°  are  of  interest  in  this  connection. 
He  found  spontaneous  lesions  of  the  kidney  and  liver  in  a  large  proportion  of  guinea 
pigs  examined.  The  greater  susceptibility  to  caffein  of  guinea  pigs  Nos.  39,  40,  49, 
is  probably  due  therefore  to  some  pathological  change  which  increased  its  toxicity. 
About  0.2  to  0.24  gram  per  kilo  may  therefore  be  regarded  as  the  minimum  lethal 
dose  for  the  normal  guinea  pig  when  caffein  is  introduced  subcutaneously,  the  mini- 
mum toxic  dose  being  about  150-160  mg  per  kilo. 


ACUTE   INTOXICATION^ — GUINEA  PIGS.  47 

Exp>eriments  were  also  conducted  to  determine  the  largest  dose  which  does  not  pro- 
duce any  vi^^iblo  effects.  In  a  number  of  tests  \vith  from  100  to  120  mg  caffein  per 
kilo  (series  E,  see  Table  6,  p.  51)  no  manifestation  of  nervous  or  muscular  disturbance 
nor  any  departure  from  the  normal  in  respiratory  activity  was  observed.  Such 
quantities  may  be  regarded  as  the  largest  doses  which  are  surely  safe  for  these  animals. 
It  is  qnito  possible,  therefore,  that  the  greater  variation  in  the  toxicity  of  caffein 
observed  in  these  exi)eriments  is  due  to  morbid  conditions.  Moreover,  there  is  some 
evidence  that  caffein  increases  the  toxicity  of  certain  poisons,  as  shown  by  Hale'"  for 
acetanilid.  Is  it  not  possible  that  caffein  may  similarly  be  affected  by  poisons  cir- 
culating within  the  body?  Indeed  the  recent  work  of  Loeb  ^'  makes  this  supposition 
highly  probable.  This  investigator  found  that  caffein  and  adrenalin  injected  together 
produce  myocarditis  in  the  rabbit.  It  ia  conceivable  that  the  combined  action  of 
caffein  and  some  preexisting  poison  may  cause  changes  which  terminate  in  the  death 
of  the  animal.  The  delayed  death  of  guinea  pigs  after  the  administration  of  caffein 
observed  in  this  and  other  series  may  probably  be  accounted  for  in  this  way. 

Experiment  57  lends  some  support  to  this  view.  The  condition  of  the  kidneys  and 
the  presence  of  a  severe  gastro-enteritis  are  sufficient  to  account  for  the  death  of  this 
case.  Again  the  frequent  association  of  gastro-enteritis  and  congestion  of  the  organs 
in  caffein  intoxication  iound  in  different  animals  makes  it  highly  probable  that  these 
lesions  were  caused  by  caffein. 

INJECTION  INTO  THE  PERITONEAL.  CAVITT. 

The  experiments  were  carried  out  with  different  doses.  All  the  guinea  pigs  in 
this  series  were  kept  on  a  uniform  diet,  consisting  of  oats .  Most  of  them  were  of  average 
size  and  there  were  no  wide  variations  in  their  weights.  The  experiments  of  series  A 
with  the  smallest  doses  were  conducted  in  March  and  April;  all  the  other  experiments 
it  will  be  noticed  were  made  in  October. 

Series  A. 

Guinea  pig  41-     Weight,  700  grams.    Diet,  oats. 

April  1:  3.30  p.  m.,  4.5  cc  2  per  cent  caffein  (130  mg  per  kilo)  injected  into  peri- 
toneal cavity.     5.35  p.  m.,  symptoms  present  but  no  tetanus. 

April  2:  Found  dead  about  2  p.  m.,  duration  of  life  about  22  hours.  Autopsy: 
Subcutaneous  hemorrhage  at  the  point  of  inoculation;  serious  exudate  on  visceral 
and  parietal  peritoneum  with  marked  inflammation  of  peritoneum;  portions  of 
intestines  showed  slight  enteritis. 

Guinea  pig  49.     Male.     Weight,  370  grams.    Diet,  oats. 

April  1:  3.15  p.  m.,  2.5  cc  2  percent  caffein  (135  mg  per  kilo)  injected  into  the  peri- 
toneal cavity;  5.30  p.  m.,  symptoms  present;    reflexes  increased,  but  no  tetanus. 
Guinea  pig  survived. 
Guinea  pig  47.     Female.     Weight,  550  grams.    Diet,  oats  since  about  Fehruary  4- 

March  17:  3.30  p.  m.,  3.5  cc  2  per  cent  caffein  (127  mg  per  kilo)  injected  into  peri- 
toneal cavity;  4.35  p.  m.,  increased  irritability  present,  but  not  marked;  5.40  p.  m., 
symptoms  about  the  same  as  before. 

March  18:  2.30  p.  m.,  condition  good;  no  symptoms.    Survived. 
Guinea  pig  ,50.     Female.     Weight,  290  grams.    Diet,  oats. 

April  1:  3.30  p.  m.,  2  cc  2  per  cent  caffein  (138  mg  per  kilo)  injected  into  peritoneal 
ca\'ity;  5.35  p.  m.,  symptoms  present;  reflexes  much  increased,  but  no  tetanus. 
Survived. 

Series  B. 

Guinea  pig  51.      Yellow  female .     Weight,  415  grams. 

October  1:  9.50  a.  m.,  3  cc  (144  mg  per  Idlo)  2  per  cent  caffein  injected  into  peri- 
toneal cavity;  4.30  p.  m.,  no  symptoms,  although  under  observation  all  day. 

October  3:  2  p.  m.,  alive. 
Guinea  pig  52.     White  male.     Weight,  450  grams. 

October  1:  9.45  a.  m.,  3.5  cc,  2  per  cent  caffein  (155  mg  per  kilo),  injected  into 
peritoneal  cavity;  4.30  p.  m.,  no  symptoms  developed  since  injection. 

October  3:  2  p.  m.,  auve. 


48  THE   TOXICITY   OF   CAFFEIN. 

Guinea  pig  53.     Brown  and  rvhite  male.     Weight,  490  grams. 

October  1:  9.45  a.  m.,  4  cc,  2  per  cent  caffein  (163  mg  per  kilo),  injected  into  peri- 
toneal cavity;  4.30  p.  m.,  no  symptoms  developed  since  injection. 

October  3:  2  p.  m.,  alive. 

October  8:  Found  dead.  Autopsy:  Congestion  of  lungs,  spleen,  liver,  kidneys,  and 
small  intestines. 

Series  C. 

Guinea  pig  59.     Gray  and  white.     Weight,  375  grams.     Di£t,  oats. 

October  3:  2  p.  m.,  3.75  cc  (0.2  gram  per  kilo)  injected  into  peritoneal  cavity;  2.15 
p.  m.,  reflexes  increased  but  not  markedly;  4  p.  m.,  reflexes  still  more  increased; 
no  other  symptoms;  5.30  p.  m.,  no  symptoms. 

October  4:  8.50  a.  m.,  guinea  pig  alive  and  active. 
Guinea  pig  58.    Brown  and  ivhite.     Weight,  380  grams.    Diet,  oats. 

October  3:  2  p.  m.,  3.8  cc  caffein  (0.2  gram  per  kilo),  2  per  cent  solution,  injected 
into  peritoneal  cavity;  2.10  p.  m.,  bind  legs  extended,  then  tetanus;  attack  lasted  a 
few  seconds,  after  which  pig  raised  himself  on  his  legs,  but  reflexes  remained  much 
exaggerated;  4  p.  m.  to  5.30  p.  m.,  no  symptoms  of  caffein  intoxication. 

October  4:  8.50  a.  m.,  guinea  pig  alive  and  active. 
Guinea  pig  56.    Gray  and  white  male.    Weight,  440  grams.    Diet,  oats. 

October  1:  11.30  a.  m.,  received  4.6  cc  of  2  per  cent  caffein  solution  (0.2  gram  per 
kilo)  into  abdominal  cavity;  11.45  a.  m.,  stiffness  and  rigidity  of  posterior  extremi- 
ties, reflexes  increased;  12.30  p.  m.,  hind  legs  paralyzed,  reflexes  increased;  4.35 
p.  m.,  no  symptoms,  guinea  pig  in  good  condition. 

October  3:  Still  alive,  in  good  condition. 

October  14:  Died.    Autopsy:  Anterior  lobe  of  right  lung  hepatized.     Small  portion 
of  small  intestine  edematous.     Other  organs  normal. 
Guinea  pig  55.     White  and  yellow  vnale.     Weight,  690  grams.    Diet,  oats. 

October  1:  11.30  a.  m.,  received  6.5  cc  of  2  per  cent  solution  caffein  (188  mg  per 
kilo)  into  peritoneal  cavity;  11.40  a.  m.,  stiffness  in  all  extremities,  reflexes  markedly 
increased;  12.30p.  m.,  reflexes  increased,  anterior  and  posterior  extremities  paralyzed; 
3  p.  m.,  found  dead. 

Series  D. 

Guinea  pig  67.    Gray  and  yellow  male.     Weight,  330  grams.    Diet,  oats. 

October  5:  11.25  a.  m.,  4  cc  of  2  per  cent  caffein  injected  into  peritoneal  cavity 
(240  mg  per  kilo);  11.30  a.  m.,  tetanus — survived,  convulsions  off  and  on.     Death 
at  2.55  p.  m.    Autopsy:  Severe  gastroenteritis;  kidney  petechiated;  congestion  of 
lungs  and  liver. 
Guinea  pig  63.    Gray  and  white  male.     Weight,  340  grams.    Diet,  oats. 

October  5:  11.20  a.  m.,  4  cc  of  2  per  cent  caffein  (235  mg  per  kilo)  injected  into 
peritoneal  cavity. 

October  14:  Alive  and  in  good  condition. 
Guinea  pig  64.    Brown  and  black  female.     Weight,  305  grams. 

October  5:  11.35  a.  m.,  3.8  cc  2  per  cent  solution  caffein  (250  mg  per  kilo)  injected 
into  peritoneal  cavity;  11.40  a.  m.,  tetanus — survived,  convulsions  off  and  on,  died 
at  4.15  p.  m.    Autoj)sy:  Findings  exactly  the  same  as  in  No.  67. 

Examination  of  the  results  of  the  experiments  by  intraperitoneal  injections  showed 
that  0.2  gram  caffein  per  kilo  was  toxic  in  two  guinea  pigs  (Nos.  59  and  58).  Severe 
symptoms  were  observed  within  15  minutes  in  No.  56  and  within  one  hour  in  No. 
55  after  the  administration  of  approximately  the  same  dose  of  caffein.  One  of  these 
died  within  three  and  one-half  hours;  the  other.  No.  56,  made  a  good  recovery  from 
the  acute  effects.  This  amount  of  caffein  may  be  regarded,  therefore,  as  the  mini. 
mum  toxic  dose  for  the  guinea  pig  when  injected  into  the  peritoneal  cavity.  This 
ia  corroborated  by  the  experiments  of  series  B  in  which  smaller  doses  failed  to  show 
any  muscular,  nervous,  or  respiratory  symptoms,  nor  were  there  any  after  effects 
noticed,  as  all  of  them  survived  and  were  kept  under  observation  for  some  time. 
The  guinea  pigs  of  series  A,  however,  seem  to  contradict  these  results.  It  will  be 
remarked  that  appreciably  smaller  doses  induced  symptoms  in  all  of  them,  and  one 
case  terminated  fatally.  The  seasonal  variation,  as  already  pointed  out,  is  in  all 
probability  likewise  responsible  for  the  difference  in  the  resistance  between  the 


ACUTE    INTOXICATION GUINEA  PIGS.  49 

guinea  piga  of  series  A  and  B.  Testa  were  made  also  to  determine  the  minimum 
fatal  dose.  For  this  purpose  the  experiments  of  series  D  were  performed.  The 
resistance  of  No.  63  in  this  series  is  quite  striking.  We  are  unable  to  explain  such 
a  discrepancy  in  the  results  obtained  under  practically  uniform  conditions.  The 
minimum  fatal  dose  of  caffein,  when  injected  into  the  peritoneal  cavity,  Ls  therefore 
about  240  to  250  milligrams  per  kilo.  These  amounts,  it  will  be  observed,  were 
rapidly  fatal,  in  striking  contrast  to  the  results  obtained  when  such  doeea  were  injected 
Bubcutaneously.  This  is  probably  due  to  a  better  absorption  from  the  peritoneal 
cavity  than  from  the  subcutaneous  tissues. 

ADMINISTRATION  BY  MOUTH. 

All  the  guinea  pigs  in  these  experiments  were  kept  on  a  diet  of  hay  and  oats  and 
were  of  large  size.    The  tests  were  made  with  different  doses  of  caffein  in  order  to 
determine  the  limits  of  toxicity  when  the  drug  was  administered  by  mouth. 
Guinea  pig  12Q.     White  and  black  male.     Weight,  855  grams.     Diet,  oats  and  hay. 

June  6:  2.20  p.  m.,  12  cc  of  2  per  cent  caffein  (0.28  gram  per  kilo)  by  mouth;  3 
p.  m.,  reflexes  increased;  5  p.  m.,  reflexes  still  more  increased;  no  other  sj-mptoms. 

June  7:  9  a.  m.,  found  dead;  guinea  pig  passed  75cc  urine,  which  was  almost  color- 
less.   Autopsi/:  Heart  and  blood  vessels  injected;  lungs  congested;  small  intestines 
congested;  other  organs  apparently  normal. 
Guinea  pig  ISO.     Black  and  brown  male.     Weight,  800  grams.     Diet,  oats  and  hay. 

June  6:  2.30  p.  m.,  12  cc  of  2  per  cent  caffein  (0.3  gram  per  kilo)  administered  by 
mouth;  3  p.  m.,  reflexes  increased;  5  p.  m.,  increase  of  reflexes  greater  than  at  3 
p.  m. 

June  7:  9  a.  m.,  found  dead;  only  a  few  cubic  centimeters  of  urine  passed  since 
4  p.  m.    Autopsy:  Heart  and  blood  vessels  injected;  lungs  congested;  small  intes- 
tines congested  slightly. 
Guinea  pig  l.U.     White  and  yellow  male.     Weight,  860  grams.     Diet,  oats  and  hay . 

June  6:  2.40  p.  m.,  12  cc  2  per  cent  caffein  administered  by  mouth;  3  p.  m.,  reflexes 
increased;  5  p.  m.,  reflexes  still  more  marked. 

June  7:  9  a.  m.,  found  dead,  pig  passed  about  5  cc  urine  since  4  p.  m.  of  previous  day. 
Autopsy:  Same  as  in  No.  130. 
Guinea  pig  136.     White  and  black  male.     Weight,  1,000  grams.     Diet,  oats  and  hay. 

June  9:  4  p.  m.,  7.5  cc  2  per  cent  caffein  solution  injected  subcutaneously  into  the 
back;  4.50  p.  m.,  reflexes  increased. 

June  10:  9.30  a.  m.,  more  sensitive  than  normal  guinea  pigs,  but  reflexes  not  quite  so 
marked  as  at  5  p.  m.  previous  day,  about  15  cc  urine  passed  since  caffein  was  injected, 
reduction  of  Fehling's  solution  considerable,  no  albumin. 

June  13:  Alivo  and  in  good  condition.     Appetite  good.     (Note. — Parallel  test  with 
urine  from  two  guinea  pigs  which  did  not  receive  caffein  failed  to  show  reduction  of 
Fehling's  solution.) 
Guinea  pig  137.     White  and  broun  male.     Weight,  925  grams.    Diet,  oats  and  hay. 

June  9:  4  p.  m.,  7  cc  2  per  cent  solution  caffein  injected  subcutaneously;  4.50  p.  m., 
reflexes  increased. 

June  10:  Reflexes  less  marked  than  at  5  p.  m.  previous  day,  but  is  more  sensitive 
than  normal  guinea  pig,  about  10  cc  urine  passed  since  injection  of  caffein,  moderate 
amount  of  reduction  of  Fehling's  solution. 

June  13:  Guinea  pig  alive,  appetite  good,  condition  good. 

June  16:  9  a.  ra.,  found  dead. 
Guinea  pig  135.     White  and  black  male.     Weight,  955  grams.     Diet,  hay  and  oats. 

June  9:  3  p.  m.,  7.5  cc  2  per  cent  caffein  solution  given  by  mouth  through  stomach 
tube;  4.50  p.  m.,  reflexes  increased. 

June  10 :  Keflexes  less  than  on  prex-ious  day  and  less  marked  than  in  No.  136,  a  few 
cubic  centimeters  dirty  brown  urine  collected  but  could  not  be  tested  for  reduction. 

June  13:  Condition  good,  appetite  good. 

June  16:  9  a.  m.,  found  dead. 
Guinea  pig  134.     White  and  brown  male.     Weight,  740  grams.     Diet,  hay  and  oats. 

June  9:  2.55  p.  m.,  6  cc  warm  2  per  cent  caffein  solution  given  by  mouth  through 
stomach  tube;  4.50  p.  m.,  reflexes  increased. 

18594°— Bull.  148—12 4 


50  THE   TOXICITY    OF    CAFFEIN. 

June  10:  9.30  a.  m.,  reflexes  much  lesa  than  day  before,  increase  slight,  a  few  cubic 
centiraeters  of  urine  passed  since  injection  of  caffein,  looked  brown  and  dirty,  could 
not  be  tested  for  reducing  substances. 

June  13:  Guinea  pig  alive,  appetite  good,  condition  good. 

June  14:  9  a.  m.,  found  dead. 
Guinea  pig  128.     White  and  black  male.     Weight,  1,075  grams.     Diet,  hay  and  oats. 

June  7:  10  a.  m.,  11  cc  2  per  cent  caffein  by  mouth  through  stomach  tube;  11.10 
a.  m.,  no  symptoms,  no  urine  passed;  1  p.  m.,  increased  reflexes,  about  15  cc  (esti- 
mated) lu-ine  passed;  4  p.  m.,  reflexes  increased,  still  more  urine  passed  (about  20  cc); 
4.50  p.  m.,  tetanus,  frequent  attacks,  then  paralysis  and  death  at  4.58  p.  m.  Autopsy: 
Lungs  congested;  blood  vessels  of  heart  injected;  intestines  slightly  congested;  fatty 
liver. 
Guinea  pig  126.     White  and  gray  male.     Weight,  980  grams.    Diet,  oats  and  hay. 

June  7:  9.40  a.  m.,  9.8  cc  2  per  cent  caffein  given  by  mouth  through  stomach  tube; 
10  a.  m.,  no  symptoms;  11.10  a.  m.,  no  m'ine  passed,  reflexes  increased;  1  p.  m.,  more 
sensitive  than  before;  4  p.  m.,  increase  of  reflexes  more  marked,  no  urine  passed;  4.45 
p.  m.,  about  15  cc  urine  collected;  5  p.  m.,  no  change. 

June  8:  9  a.  m.,  reflexes  about  the  same  as  5  p.  m.  previous  day,  no  urine  passed 
since  4.45  p.  m.  previous  day,  considerable  reduction  of  Fehling's  solution,  much  more 
than  ui'ine  of  guinea  pig  No.  127;  11.05  a.  m.,  convulsions;  12  noon,  still  alive  and 
stretched  out  on  abdomen;  died  at  1  p.  m.  Autopsy:  Lungs  badly  congested;  heart 
and  blood  vessels  injected;  blood  vessels  of  kidney  and  of  small  intestines  injected; 
liver  engorged  with  blood;  a  few  necrotic  spots  in  stomach. 
Guinea  pig  127 .     White,hlach,  and  brown  male.     Weight,  760  grams.    Diet,  oats  and  hay. 

June  7:  9.50  a.  m.,  7.6  cc  2percentcaffeinby  mouth  through  stomach  tube;  10  a.  m., 
no  symptoms;  11.10  a.  m.,  reflexes  increased,  no  urine  passed;  1  p.  m.,  very  sensitive; 
4  p.  m.,  sensitiveness  increased,  about  20  cc  xudne  passed;  5  p.  m.,  no  change. 

June  8:9  a.  m.,  reflexes  about  the  same  as  5  p.  m.  previous  day;  9.30  a.  m.,  guinea 
pig  passed  30  cc  urine  since  he  received  caffein,  urine  showed  a  moderate  amount  of 
reduction;  12  noon,  convulsions;  died  at  2.30  p.  m.  Autopsy:  Lungs  congested; 
blood  vessels  of  heart  and  of  intestines  injected;  numerous  necrotic  spots  in  stomach; 
other  organs  apparently  normal. 

Examination  of  the  protocols  shows  that  the  absorption  of  caffein  from  the  gastro- 
intestinal canal  was  quite  rapid,  symptoms  having  been  observed  as  early  as  20  min- 
utes after  its  introduction.  The  duration  of  life,  it  will  be  remarked,  varied  with  the 
size  of  the  dose.  When  approximately  3  decigrams  per  kilo  were  fed,  all  the  animals 
died  in  the  night.  They  lived,  therefore,  less  than  18  hours.  Two  decigrams  per  kilo 
were  likewise  fatal,  but  the  duration  of  life  was  longer.  To  decide  whether  or  not  this 
is  the  smallest  fatal  dose,  smaller  amounts  were  fed.  It  seemed  at  first  that  about  150 
mg  per  kilo  was  the  smallest  toxic  dose,  and  about  200  mg  per  kilo  the  minimum  fatal 
dose.  Macroscopic  examination  of  the  organs,  however,  threw  some  doubt  on  this 
supposition,  for  well-marked  lesions  were  noticed  in  all  of  the  guinea  pigs  which 
received  0.2  gram  per  kilo.  It  is  quite  possible,  therefore,  that  the  minimum  fatal 
dose  may  be  somewhat  higher,  as  we  have  reason  to  believe  that,  at  least  in  some  patho- 
logic conditions,  the  susceptibility  to  caffein  is  increased.  The  presence  of  fatty 
changes  in  the  liver  of  No.  128  and  the  rapid  death  in  this  case  lends  especial  support 
to  this  view.  Hence,  the  minimum  fatal  dose  is  probably  greater  than  0.2  gram  per 
kilo  for  the  normal  guinea  pig.  The  doses  employed  for  the  tests  on  guinea  pigs  Nos. 
129, 130,  and  131  may  be  considered  therefore  the  minimum  fatal  dose  for  these  animals. 
It  will  be  also  remarked  that  macroscopical  examination  of  the  organs  of  these  animals 
failed  to  reveal  the  presence  of  severe  lesions.  That  the  minimum  toxic  dose  is  prob- 
ably much  smaller  than  0.28  gram  per  kilo  is  indicated  by  the  experiments  on  guinea 
pigs  Nos.  135  and  134,  in  which  0.15  gram  caffein  per  kilo  induced  mild  symptoms 
in  from  two  to  three  horns.  Both  of  these,  however,  and  also  No.  137  died  io\xr  to  six 
days  after  the  drug  was  fed.  As  already  pointed  out,  caffein  may  be  a  factor  in  the 
delayed  death  of  guinea  pigs  which  received  moderate  doses  of  it.  That  this  suppo- 
sition may  also  be  true  for  guinea  pigs  Nos.  134, 135,  and  137  is  indeed  made  probable 
by  the  observation  that  after  moderate  amounts  of  caffein  symptoms  may  persist  in 
the  guinea  pig  for  about  24  hours,  and  also  by  the  fact  that  the  secretion  of  urine  in 


ACUTE  INTOXICATION GUINEA  PIGS. 


51 


these  animals  was  very  scanty,  as  shown  in  the  preceding  record  of  the  experiraenta; 
this  means  slow  elimination  of  caffein  and  iLs  produrta  of  decomposition.  It  is  con- 
ceivable that  the  presence  of  toxic  amounts  of  caffein  in  the  body  for  a  considerable 
length  of  time  would  induce  changes  that  ultimately  lead  to  the  death  of  the  animal 
or  that  morbid  processes  are  set  up  by  the  combined  action  of  caffein  and  some  pre- 
existing poinon.  Since  some  guinea  pigs,  however,  survived  the  doses  indicated,  it 
is  more  probable  that  such  changes  would  be  brought  about  by  caffein  in  the  presence 
of  a  preexisting  poison.  The  death  of  these  pigs,  and  also  of  No.  137  several  days  later, 
is  difficult  to  account  for  on  any  other  theory  -than  the  one  suggested.  Were  it  not  for 
the  fact  that  controls,  that  is,  animals  of  the  same  lot  which  had  not  received  caffein 
survived  all  of  the  experimental  animals,  changed  conditions  of  environment  or  acci- 
dent might  be  considered  the  cause  of  death  in  the  guinea  pigs  of  the  last  series. 

Table  6. — Subcutaneous  injection  of  guinea  pigs. 
SERIES  A. 


Num- 
ber of 
pig- 

Weight. 

Callein 
per 
kilo. 

.\ppearance  of 
symptoms. 

Duration  of  life. 

Diet. 

Month. 

Remarks. 

18 

Grams. 
500 
548 
442 

Gram. 

0.300 

.290 

.360 

2  minutes 

2  hours  40  minutes.. 
30  minutes 

Carrots 

Oats 

March 

...do 

Female. 

15 

Do. 

14 

15  minutes.. 

..do 

.do 

.do 

Do. 

SERIES  B. 


497 

0.200 

570 

.210 

820 

.200 

618 

.194 

850 

.200 

2  hours  20  minutes. 

25  minutes 

1  hour  25  minutes. , 


1  hour  30  minutes. 


3  hours  30  minutes. 
2  hours  15  minutes. 
Less  than  18  hours. 


25  hours. 
18  hours. 


Oats 

Carrots 

Carrots  and 

oats. 

Oats 

Carrots  and 

oats. 


April 

February 
..do 


March 

February 


Female. 
Male. 
Do. 

Female. 
Male. 


SERIES  C. 


510 

0.200 

510 

.200 

320 

.219 

3.50 

.200 

785 

.200 

585 

.200 

330 

.240 

335 

.238 

545 

.238 

540 

.240 

560 

.232 

None 

do 

1  hour  15  minutes. 

do 

25  minutes 

20  minutes 

1  hour  30  minutes. 

1  hour 

50  minutes 

45  minutes 

35  minutes 


5  days 

Survived 

Within  18  hours.... 

About  2i  days 

Less  than  22  hours. 

9  days 

Less  than  24  hours. 

do 

About  2  days 

do 

About  3  days 


Oats 

do 

do 

do 

do 

do 

do 

do 

do 

do 

do 


October. 

..do 

..do 

..do 

..do 

..do 

..do 

..do 

..do 

..do 

..do 


Male. 

Do. 
Female. 

Do. 
Male. 

Do. 
Female. 

Do. 
Male. 

Do. 

Do. 


SERIES  D. 


49 

510 
630 

435 

820 

660 
470 

0.160 
.158 

.160 
,150 

.150 
.170 

1  hour  40  minutes.. 

Less  than  18  hours. . . 
Less  than  2  days 

Survived 

Oats 

March 

February  . 

March 

February . 

...do 

Male. 

40 

Oats  and 
carrots. 

Oats 

Oats  and 

carrots. 
do 

Do. 

45 

None 

Female. 

39 

2  days 

Male. 

41 

Survived 

46 

1  hour  20  minutes. . 

do 

Oats(?) 

March 

Female. 

SERIES  E. 

19 

556 
4C)0 
430 
5:55 
330 
520 

0.100 
.120 
.116 
.112 
.100 
.100 

Survived 

Oats 

do 

April 

February  . 
...do 

42 

None 

.do 

43 

do 

do 

do 

do 

44 

do 

do 

...do 

97 

do 

do 

do 

November 
...do 

98 

do 

About  3  days 

Carrots 

52 


THE  TOXICITY   OF   CAFFEIN". 


Table  7. — Injection  into  peritoneal  cavity;  guinea  pigs. 

SERIES  A. 


Num- 
ber of 
pig- 

Weight. 

Caflein 
per 
kilo. 

Appearance  of 
symptoms. 

Duration  of  life. 

Diet. 

Month. 

Remarks. 

41 

Grams. 
700 
370 
550 
290 

Gram. 

0.130 

.135 

.127 

.138 

2  hours 

22  hours 

Oats 

do 

April 

.do 

Male 

49 

2  hours  15  minutes. 
1  hour 

Survived 

Do. 

47 

do 

do 

March 

April 

50 

do 

.do 

Do 

SERIES  B. 


415 

0.144 

450 

.155 

490 

.163 

None.. 

do. 

do. 


Survived. 

do.... 

do.... 


Oats . . . 
....do. 
....do. 


October. 

..do 

..do 


SERIES  C. 


375 

0.200 

380 

.200 

440 

.200 

690 

.188 

15  minutes. 

10  minutes. 
15  minutes. 
1  hour 


Survived. 


do 

14  days 

3  hours  30  minutes. . 


Oats. 


...do. 
...do. 
...do. 


October. . 


.do. 
.do. 
.do. 


Table  8. — Caffein  by  mouth;  guinea  pigs. 
SERIES  J. 


SERIES  D. 

67 

330 
340 
305 

0.240 
.235 
.250 

5  minntps 

30  minutes. 

Oats 

.do 

October. . . 
.do 

Male. 

63 

Survived. 

Do. 

64 

25  minutes 

4  hours  40  minutes. . . 

do 

...do 

Female. 

Caflein 

Weight. 

per 

kilo. 

Grams. 

Gram. 

855 

0.280 

800 

.300 

800 

.280 

955 

.  150 

740 

.KM 

925 

.1.50 

1,000 

.150 

980 

.200 

760 

.200 

1,075 

.200 

Appearance  of 
symptoms. 


Duration  of  life. 


Diet. 


Month. 


40  minutes 

.30  minutes 

20  minutes 

1  hour  50  minutes. 

3  hours 

SO  minutes 

do 

20  minutes 

1  hour 

3  hours 


Less  than  8  hours. . 
Less  than  18  hours. 

do 

6  days 

4  days 

6  days •.■.-. 

Survived 

27  hours 

28  hours 

7  hours 


Hay  and  oats 

do 

....do 

do 

do 

....do 

....do 

....do 

....do 

....do 


June . 
...do.. 

..do.. 
...do.. 

..do.. 
...do.. 

..do.. 
...do.. 

..do.. 

..do.. 


'  Subcutaneous  injection  for  comparison. 


SUMMARY. 


A  survey  of  the  results  obtained  in  experiments  on  guineapigs  shows  that  the  mode 
of  introduction  of  caffein  exerts  but  little  influence  on  its  toxicity.  On  careful  analy- 
sis it  will  be  observed  that  the  rate  of  absorption  after  the  administration  of  caffein  by 
mouth,  subcutaneously,  or  intraperitoneally  is  about  the  same  for  the  time  of  appear- 
ance of  symptoms.  The  persistence  of  the  symptoms  of  caffein  intoxication  observed 
in  these  experiments  for  24  hours  after  administration  points  to  slow  elimination, 
which  may  be  expected,  owing  to  the  fact  that  the  guinea  pigs  passed  but  little  urine 
and  caffein  is  not  diuretic  for  these  animals.  The  prolonged  presence  of  caffein 
in  the  body  probably  exerts  a  harmful  influence  or  after  effect,  which  may  account 


ACUTE  INTOXICATION CATS.  53 

for  tho  delayed  death  of  annw  animals  many  days  after  a  single  dose  of  caffein  was  given. 
Among  the  factors  which  undoubtedly  influence  toxicity,  season  should  be  considered, 
while  tho  presence  of  a  diseased  condition  undoubtedly  tends  to  decrease  the  resist- 
ance of  the  guinea  pig  to  caffein.  Diet  was  without  any  influence  on  the  toxicity  of 
the  single  dose  of  caffein. 

EXPERIMENTS  ON  CATS. 

These  experiments  were  performed  on  well-fed  animals  which  were  kept  under 
observation  for  several  days  before  the  testa  with  caffein  were  made.  The  diet  con- 
sisted of  meat  exdu.sively.  In  some  cases  tho  urine  was  examined  for  albumin  and 
sugar  before  caffein  was  given.  No  test.s  ^\^th  caffein  were  made  if  large  amount.s  of 
albumin  were  found.  It  may  be  remarked  that  sugar  was  never  found  in  cats  before; 
the  administration  of  caffein,  but  that  considi'rablo  amounts  of  it  were  found  in  some 
cases  after  it  was  givi-n.  Studies  by  various  modes  of  administration  were  made,  by 
subcutaneous  injection,  intraperitoneally,  or  by  mouth.  Attention  waa  also  directed 
to  the  resistance  to  caffein  in  young  cats,  several  experiments  on  kittens  being  made 
with  this  object  in  view. 

SUBCTTTANEOTTS  IXJECTION. 

Rost  stated  that  caffein  is  eliminated  in  the  urine  unchanged  after  its  introductinn 
into  the  body  and  that  the  amounts  found  varied  with  different  species  of  animals. 
In  the  rabbit  the  amount  eliminated  was  about  21  per  cent;  in  the  dog  about  8  per  cent ; 
and  in  the  cat  somewhat  less  than  2.5  per  cent.  It  would  appear,  therefore,  that  the 
cat  decomposes  caffein  more  readily  than  the  rabbit  or  dog;  its  resistance  consequently 
ought  to  be  greater  than  that  of  the  other  animals.  Moderately  large  doses  were  accord- 
ingly employed  in  the  preliminary  experiments  (series  A),  but  the  results  obtained,  as 
shown  in  the  protocols,  indicated  that  caffein  is  fully  as  toxic  fur  the  cat  as  for  the 
rabbit  or  dog.  The  doses  were  then  decreased  and  experiments  were  performed  in 
order  to  ascertain  the  smallest  toxic  as  well  as  the  smallest  fatal  dose. 

Series  A 

Three  decigrams  of  caffein  per  kilo  were  administered  in  these  experiments.  The 
results  are  shown  in  the  following  protocols: 

Cat  4-     Black  and  white.     Weight,  1,440  grams. 

May  26:  10.05  a.  m.,  22  cc  2  per  cent  caffein  (0.3  gram  per  kilo)  injected  subcuta- 
neously;  11.10  a.  m.,  copious  salivation,  cat  irritable,  muscular  stiffness  present,  but 
no  tetanus;  11.45  a.  m.,  cat  restless,  convulsions,  attacks  of  short  duration,  no  paralysis 
observed  after  the  convulsions,  pupils  dilated;  4.45  p.  m.,  cat  quiet,  slight  paralysis 
present. 

May  27:  Cat  exhausted. 

May  28:  Found  dead. 
Cat  5.     Black  and  ivhite  male.     Weight,  1,396  grams. 

June  3:  10  a.  m.,  21  cc  of  2  per  cent  caffein  (0.3  gram  per  kilo)  injected  subcuta- 
neously;  12  noon,  found  dead. 

Although  there  was  considerable  difference  in  the  duration  of  life  following  the 
injection  of  the  same  dose  of  caffein  per  kilo,  the  final  outcome  was  the  same,  as  both 
cats  died  from  the  effects  of  the  drug.  One  died  within  2  hours  and  the  other  lived 
more  than  30  hours  after  its  administration.  Three  decigrams  of  caffein  per  kilo  is, 
therefore,  surely  fatal  to  these  animals.  Tests  made  with  smaller  doses  are  shown  in 
the  following  experiments: 

Series  B. 

In  these  experiments  the  doses  employed  ranged  between  0.20  and  0.25  gram  caffein 
per  kilo. 


54  THE   TOXICITY   OF   CAPFEIN". 

Cat  3.    Black  and  wMte  female.     Weight,  2,854  grams.     Well  fed. 

June  4:  10.30  a.  m.,  35  cc  2  per  cent  caffein  (0.25  gram  per  kilo)  injected  subcuta- 
neously;  11  a.  m.,  found  dead. 

Cat  6.    Black  and  tuhite.     Weight,  1,645  grams. 

June  3:  20  cc  2  per  cent  caffein  (0.243  gram  per  kilo)  injected  subcutaneously  at  3 
p.  m.,  cat  grew  very  irritable  in  a  few  minutes;  about  4.  p.  m.  reflexes  decidedly 
increased;  5  p.  m.,  cat  paralyzed. 

June  4:  Cat  found  dead. 
Cat  8.     Weight,  1,735  grams. 

October  7:    4  p.  m.,  22  cc  2  per  cent  caffein  (0.25  gram  per  kilo)  injected  subcuta- 
neously in  the  back;  4.30  p.  m.,  cat  irritable,  salivation  profuse,  convulsions;  died  at 
5.30  p.  m. ;  no  urine  passed  after  caffein  was  given. 
Cat  9.     Weight,  1,960  grams. 

October  7:  3.45  p.  m.,  25  cc  2  per  cent  caffein  (0.25  gram  per  kilo)  injected  subcuta- 
neously in  the  back;  4.45  p.  m.,  cat  very  irritable,  repeated  attacks  of  convulsions, 
salivation  copious;  died  at  5.30  p.  m.;  cat  did  not  urinate  after  injection  of  caffein. 
Cat  12.    Striped  kitten.     Weight,  1,185  grams. 

October  9:  Urine  examined,  no  albumin,  no  sugar;  1.45  p.  m.,  12  cc  2  per  cent 
caffein  administered;  5  p.  m.,  cat  alive,  no  symptoms  except  salivation  and  general 
irritability.  .. 

October  10:  10.30  a.  m.,  found  dead.    About  15  cc  urine  collected,  but  no  examina- 
tion made. 
Cat  14-    Black.     Weight,  1,855  graTns.  > 

October  8:  1.40  p.  m.,  18.5  cc  2  per  cent  caffein  (0.2  gram  per  kilo);  3  p.  m.,  cat 
became  restless  about  10  minutes  after  caffein  was  injected;  cried  persistently  and 
moved  about  in  cage,  no  convulsions,  cat  urinated  about  15  cc,  cat  defecated. 

October  9:  9  a.  m.,  cat  found  dead  in  cage.  Urine  gave  very  heavy  reduction  of 
Fehling's  solution  (much  more  than  was  obtained  from  urine  of  rabbits);  20  cc  urine 
analyzed  contained  4.65  per  cent  sugar.  Autopsy:  Lungs  deeply  congested;  liver 
marked  fatty  infiltration  and  degeneration;  spleen  normal;  kidneys  pale  and  anemic; 
intestines  normal;  stomach  normal. 
Cat  15.    Striped.     Weight,  2,145  gram^. 

October  8:  2  p.  m.,  22  cc  (0.2  gram  per  kilo)  2  per  cent  caffein  injected  subcutane- 
ously; 2.30  p.  m.,  cat  irritable,  restless,  trying  to  get  out  of  cage,  crying  persistently; 
2.40,  convulsions  lasting  about  two  minutes,  then  cat  raised  itself  and  made  attempts 
to  get  out  of  cage,  no  salivation,  cat  vuinated  about  10  cc  and  defecated. 

October  9:9  a.  m.,  cat  found  dead  in  cage,  about  10  cc  of  urine  contained  enormous 
quantities  of  sugar.    Autopsy:  Lungs  severely  congested;  liver  showed  marked  fatty 
degeneration;  spleen  normal;  kidneys  slightly  pale  and  anemic;  intestines  mildly  con- 
gested; stomach  normal. 
Cat  19.     White.     Weight,  1,100  grams. 

October  20:  13  cc  of  2  per  cent  caffein  (0.236  gram  per  kilo).  About  15  minutes 
later  cat  became  irritable,  reflexes  increased,  persistent  crying,  stiffness  of  extremities, 
diarrhea  present;  4.30  p.  m.,  stiffness  of  muscles,  coordination  much  disturbed,  walked 
with  great  difficulty;  4.30  p.  m.,  no  new  symptoms,  persistent  crying  continued. 

October  21:  Found  dead. 
Cat  20.    White  kitten.     Weight,  790  grams. 

October  20:  11.35  a.  m.,  10  cc  2  per  cent  caffein  (0.25  gram  per  kilo)  given  subcu- 
taneously; 12  noon,  convulsions  followed  by  paralysis;  1.30  p.  m.,  still  breathing, 
apparently  in  comatose  condition,  lay  on  its  side,  dyspnoea,  profuse  salivation;  4  p.  m., 
convulsions  and  death. 

The  results  of  the  experiments  of  series  B  show  that  a  dose  of  even  0.2  caffein  per  kilo 
is  very  toxic  for  the  cat.  Symptoms  appeared  in  one  animal  40  minutes  after  the  injec- 
tion of  caffein.  Some  of  them  were  found  dead  18  hours  after  injection,  which  means  that 
the  duration  of  life  was  probably  a  great  deal  less  since  there  was  evidence  that  they 
had  been  dead  for  some  time.  Death  occurred  quite  soon  after  larger  doses  were 
injected.  Cat  No.  3  died  30  minutes  after  it  received  caffein.  The  amounts  employed 
in  these  experiments  can  not  be  considered  therefore  as  the  minimum  fatal  doses. 
Smaller  doses  were  then  tried,  as  shown  in  the  experiments  of  the  next  series. 


ACUTE  INTOXICATION — CATS.  55 

Series  V. 

Experimenta  were  performed  on  five  cats  which  received  from  MO  to  155  mg  per  kilo, 
as  follows: 

Cat  24.    Striped.     Weight,  1,. MO  grams. 

October  25:  10  a.  m.,  50  cc  urine,  albumin  moderate  amount — no  sugar;  10  cc  caffein 
injected  subcutaneously  at  12  noon;  12.80,  irritable,  cried  persistently,  no  appetite; 
4  p.  m.,  no  convulsions,  but  persistent  crying. 

October  27 :  Cat  was  still  alive. 
Cat  17.     Weight,  2,030  grams. 

October  12:  9.30  a.  m.,  G5  cc  urine  collected;  more  than  a  trace  of  albumin  present, 
no  reduction  of  Fehling's  solution;  3  p.  m.,  20  cc  2  per  cent  caffein  (150  mg  per  kilo) 
injected  subcutaneously;  3.15  p.  m.,  irritable  and  restless. 

October  l.'i:  9  a.  m.,  about  15  cc  urine  collected,  reduction  of   Fehling'a  solution 
marked;  osazone  test  also  positive. 
Cat  23.     Black  and  white.     Weight,  J, 645  grams. 

October  25:  10  a.  m.,  140  cc  urine  collected  (since  October  23),  small  amount  of 
albumin  present,  no  sugar. 

October  27:  9  a.  m.,  no  albumin;  no  sugar  in  urine;  11.50  a.  m.,  12.5  cc  caffein  injected 
subcutaneously  (0.15  gram  per  kilo);  1  p.  m.,  convulsions  and  death. 

Cat  7.    Striped  kitten.     Weight,  1,285  grams. 

October  11:  Urine  collected,  no  albumin,  no  sugar;  9.50  a.  m.,  10  cc  2  per  cent  caf- 
fein injected  subcutaneously  in  the  back;  10.10,  violent  convulsions  lasting  about  30 
seconds;  10.20,  convulsions  of  shorter  duration;  10.30  convulsions;  10.35,  convulsions 
lasting  a  few  seconds;  urine  passed  about  10.20,  contained  a  moderate  amount  of  albu- 
min, but  there  was  no  reduction  of  Fehling's  solution;  10.45,  profuse  salivation  and 
paralysis;  died  about  10.50. 
Cat  39.      Yelloiv.     Weight,  2,285  grams. 

April  13:  2.40  p.  m.,  16  cc  2  per  cent  caffein  (0.14  gram  per  kilo)  injected  subcu- 
taneously in  the  back;  3.45  p.  m.,  cat  died. 

Of  the  five  experiments  of  this  series  three  died  after  doses  of  140,  150,  and  155  mg 
per  kilo.  The  other  two  showed  symptoms  of  toxicity,  but  survived  a  dose  of  150  mg 
per  kilo  which  indicated  that  the  minimum  fatal  dose  was  probably  reached.  To  test 
this  supposition  smaller  doses  were  administered,  as  shown  in  the  following  experi- 
ments. 

Series  D. 

Ten  cats  were  used  for  this  series  of  experiments,  and  the  doses  administered  varied 
between  103  and  139  mg  per  kilo.  The  results  shown  in  the  appended  table  (p.  — )  in- 
dicate that  about  120  to  140  mgof  caffein  per  kilo  may  induce  mild  symptoms  in  some 
cases.  The  conclusion  may  be  safely  drawn  therefore  that  150  mg  per  kilo  is  approxi- 
mately the  minimum  fatal  dose  for  the  cat  when  the  drug  is  given  subcutaneously. 
That  smaller  doses  are,  however,  by  no  means  to  be  regarded  as  always  safe  is  shown  in 
the  follo^ving  experiments. 

Series  E. 

Cat  4S.     Weight,  3,225  grams. « 

September  14: 10.20  a.  m.,  20  cc  2  per  cent  caffein  (0.124gram  per  kilo)  injected  into 
the  back;  11  a.  m.,  tetanus  and  death.    Autopsy:   Lungs  congested;  liver  congested 
and  showed  hemorrhagic  spots  in  capsules  and  fatty  degeneration;  kidneys  slightly 
congested;  other  organs  normal. 
Cat  48.    Black  female.     Weight,  3,050  grams. 

September  14: 18  cc  2  per  cent  caffein  (0.118  gram  per  kilo)  injected  subcutaneously 
in  the  back;  10.30  a.  m.,  violent  convulsions  and  death.  Autopsy:  Lungs  congested  in 
spots  showing  numerous  petechia;  liver  congested;  spleen  congested;  other  organs 
normal. 

The  diminished  resistance  to  caffein  of  cats  Nos.  43  and  48  might  be  due  to  the 
pathologic  changes  found  on  autopsy,  for  evidence  is  not  wanting  that  the  toxicity 

oCat  probably  old;  had  been  in  the  laboratory  for  several  weeks  before  the  experiment.  Gained  in 
weight  175  grams. 


56  THE   TOXICITY   OF   CAFFEIN. 

of  drugs  might  be  greatly  altered  under  pathological  conditions.  Hunt*"  has  Bhown 
that  resistance  to  acetonitril  is  considerably  diminished  in  chi-onic  alcoholism.  This 
Beems  to  be  true  also  of  other  di'Ugs  imder  abnormal  conditions.  Smaller  doses  of 
atropiu"^  are  required  in  lead  poisoning  than  under  jaormal  conditions  to  produce 
the  same  results.  The  following  experiment  is  of  interest  in  this  connection,  for  in 
this  case  a  much  smaller  dose  than  was  given  in  experiments  Nos.  43  and  48  produced 
the  typical  symptoms  of  caffein  poisoning  and  proved  to  be  fatal. 

Cat  47,  black  and  white  male.     Weight,  4,220  grams. 

September  15:  Received  sub cutaneously  18  cc  2  per  cent  oaffeia  (0.084  gram  per 
kilo) ;  no  symptoms  observed  for  about  six  hours. 

September  16:  No  symptoms. 

September  17:  Weight,  4,250  grams;  injected  18  cc  2  per  cent  caffein  (0.084  gram 
per  kilo);  tetanus  and  death  after  two  hours.  Autopsy:  Severe  hemorrhagic  pneu- 
monia; kidneys  pale,  other  organs  normal. 

Since  two  controls  survived  the  same  dose  in  proportion  to  the  body  weight  of  the 
animal  without  showing  any  symptoms,  the  assumption  is  justified  that  the  lower 
resistance  to  caffein  was  due  to  the  presence  of  pneumonia,  thus  affording  additional 
support  to  the  view  that  the  toxicity  of  caffein  may  be  increased  in  disease. 

INJECTION  INTO  THE  PERITONEAL  CAVITY.  > 

These  experiments  were  carried  out  on  full-grown  and  on  young  subjects.  As  in 
previous  experiments,  doses  of  different  sizes  were  employed.  A  dose  of  0.2  gram 
per  kilo  was  tried  first  an(>then  reduced  gradually  to  0.1  gram  per  kilo. 

Cat  10.    Female.     Weight,  2,970  grams. 

October  9,  1909:  1.30  p.  m.,  30  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected 
into  the  peritoneal  cavity;  urine  examined  for  albumin  and  sugar,  negative;  cat 
found  dead  at  2.30  p.  m.    No  urine  in  the  bladder. 
Cat  16.    Black  female.     Weight,  2,420  grams. 

October  9,  1910:  Urine  examined  for  albumin  and  sugar,  negative;  2.30  p.  m.,  22  cc 
2  per  cent  caffein  (0.183  gram  per  kilo)  injected  into  the  peritoneal  cavity;  foimd 
dead  at  3  p.  m. 
Cat  99.     Well-fed  gray  female.     Weight,  3  kilos. 

Jime  22,  1911:  3.40  p.  m.,  15  cc  2  per  cent  caffein  injected  into  peritoneal  cavity; 
salivation  and  marked  irritability  within  one  hour  after  injection. 

June  24:  Alive,  appetite  good. 
Cat  98.     Well-fed  black  male.     Weight,  4,100  grams. 

June  22:  3.45  p.  m.,  20.5  cc  2  per  cent  caffein  (0.1  gram  per  kilo)  injected  into 
peritoneal  cavity;  very  irritable  a  few  minutes  after  injection,  no  other  symptoms. 

Jime  24:  No  symptoms,  appetite  good. 
Cat  93.    Black  and  white.     Weight,  1,450  grams. 

June  22:  3  p.  m.,  30  cc  2  per  cent  caffein  (0.137  gram  per  kilo)  injected  into  peri- 
toneal cavity;  salivation,  no  other  symptoms;  under  observation  imtil  6  p.  m. 

June  23:  9  a.  m.,  no  m-ine,  cat  showed  no  symptoms. 

Jime  24:  9  a.  m.,  no  symptoms,  took  nourishment  as  usual. 
Cat  87.     Well-fed  white  female.     Weight,  2,615  grams. 

Jime  23:  2.45  p.  m.,  19  cc  2  per  cent  caffein  (0.145  gram  per  kilo)  injected  into  peri- 
toneal cavity;  became  irritable  and  restless. 

June  24:  9  a.  m.,  no  symptoms,  took  nourishment  as  usual. 
Cat  97.    Gray.    Age,  3  months.     Weight,  500  grams.    Diet,  meat. 

June  24:  2.25  p.  m.,  5  cc  2  per  cent  caffein  (0.2  gram  per  kilo)  injected  into  peri- 
toneal cavity;  4  p.  m.,  no  symptoms. 

June  29:  Died. 
Cat  96.    Gray  and  white.    Age,  3  months.     Weight,  575  grams.    Diet,  meat. 

June  24:  2.20  p.  m.,  4  cc  2  per  cent  caffein  (0.139  gram  per  kilo)  injected  into  peri- 
toneal ca^dty;  3.55  p.  m,,  no  symptoms. 

June  30:  Died. 
Cat  95.    Black.    Age,  about  3  months.     Weight,  860  grams.    Diet,  meat. 

Jime  24:  10.15  a.  m.,  8.6  cc  2  per  cent  caffein  injected  into  peritoneal  cavity,  sali- 
vation immediately  after  injection;  10.25,  convulsions  and  paralysis;  died  10.45  a.  m. 
Autopsy:  Macroscopical  examination  of  the  organs,  negative. 


ACUTE  INTOXICATION — CATS,  57 

Cat  94.    Black  and  white.     Weight,  790  yrains.     Aye,  about  d  months.     Diet,  meat. 

June  24:  10  a.  m.,  8  cc  2  per  cent  caffein  injected  into  peritoneal  cavity;  4  p.  m., 
under  continual  observation  since  injection,  cat  very  irritable,  respiration  more  rapid 
than  normal,  diarrhea  present. 

Examination  of  the  above  protocols  show  that  a  dose  of  2  decigrams  per  kilo  was 
fatal  within  one  hour  to  one  cat  and  that  a  somewhat  smaller  dose  killed  another 
individual  in  30  minutes.  Amounts  under  0.15  gram  per  kilo  were  just  sufficient  to 
induce  mild  symptoms,  such  as  increased  irritability  and  salivation,  Avhich  disap- 
peared within  a  few  hoiu^.  In  no  case  were  the  effects  noticeable  on  the  following 
day.  The  experiments  on  yomig  kittens  are  especially  interesting,  as  they  proved, 
contrary  to  expectation,  to  be  distinctly  more  resistant  than  full  grown  individuals. 
The  death  of  Nos.  97  and  96  \vithin  five  and  six  days,  respectively,  can  not  be  ascribed 
to  caffein,  since  some  of  the  controls  also  died.  Moreover,  it  will  be  remarked  in 
this  connection  that  no  symptoms  appeared  in  three  of  the  four  yomig  kittens  after 
the  administration  of  a  dose  which  was  rapidly  fatal  to  adult  cats.  The  rapid  death 
of  No.  95  after  the  same  dose  forms  an  exception  which  can  not  be  accounted  for,  as 
macroscopical  examination  at  autopsy  proved  negative. 

ADMINISTRATION  BY  MOUTH. 

Two  decigrams  per  kilo  were  given  at  first,  but  it  was  found  that  this  amount  was 
surely  fatal.  The  dose  was  therefore  reduced  to  0.125  gram  per  kilo.  In  all  of  these 
experiments  caffein  was  given  by  means  of  a  soft  rubber  patheter  slipped  over  the 
stem  of  a  funnel  which  served  as  a  stomach  tube.  A  2  per  cent  aqueous  solution  was 
used  throughout  these  tests  except  in  one  case  in  which  caffein  was  given  mixed 
with  the  food. 

Cat  92.    Black  and  ivhite  female.     Weight,  1,750  grams. 

June  10:  12.05  p.  m.,  14  cc  2  per  cent  caffein  (0.16  gram  per  kilo)  given  by  mouth; 
cat  was  quiet  when  tied  on  holder,  struggled  only  a  little  when  tube  was  put  into 
stomach;  12.30  p.  m.,  cat  vomited,  no  other  symptoms. 

Jime  13:  Condition  good,  appetite  good. 
Cat  87.     White  female.     Weight,  2,620  grams.    Diet,  meat. 

June  5:  2.15  p.  m.,  20  cc  2  per  cent  caffein  (0.15  gram  per  kilo)  solution  admin- 
istered by  mouth  through  stomach  tube;  2.30  p.  m.,  cat  irritable,  but  no  other  symp- 
toms; 5  p.  m.,  condition  about  the  same,  except  that  it  was  more  irritable  and  showed 
some  stiffness  of  the  extremities. 

June  13:  Alive  and  in  good  condition,  appetite  good,  not  irritable. 
Cat  91.     White  female.     Weight,  3,050  grams. 

Jime  10 :  12  noon,  23  cc  (0. 15  gram  per  kilo)  of  2  per  cent  caffein  administered  by  mouth, 
cat  struggled  violently;  1.30,  salivation;  1.40  p.  m.,  convulsions;  died  at  2  p.  m. 
Autopsy:  Congestion  of  limgs,  liver,  and  spleen;  heart  vessels  injected;  other  organs 
normal. 
Cat  88.    Black  and  ivhite  female.     Weight,  3,260  grams.    Diet,  m^at. 

June  5:   2.20  p.  m.,  25  cc  of  2  per  cent  caffein  (0.15  gram  per  kilo)  given  by  mouth; 
2.45  p.  m.,  cat  irritable,  no  other  symptoms  (cat  did  not  vomit  after  the  administrdtion 
of  caffem);  4  p.  m.,  cat  found  dead.     Autopsy:   Liver  very  much  congested;   heart 
contracted;  body  was  still  warm  at  the  time  of  autopsy. 
Cat  90.     White  and  yellow  female.     Weight,  2.685  grams.    Diet,  meat. 

June  5:  3.15  p.  m.,  27  cc  of  2  per  cent  caffein  (0.2  gram  per  kilo)  given  by  mouth 
through  stomach  tube,  about  half  an  hour  later  cat  became  irritable  and  began  to 
salivate;  at  4.30  p.  m.  salivation  became  more  marked,  dyspnoea  was  well  developed, 
and  the  cat  was  quite  restless  and  had  tremors;  5  p.  m.,  short  spasms  of  posterior 
extremities,  but  lay  quietly  in  the  cage  most  of  the  tmie;  5.20  p.  m.,  con\Tilsions  of 
short  duration  and  death,  muscular  relaxation  followed  immediately  after  convulsions, 
no  vomiting,  diarrhea  observed  after  administration  of  cafl'ein,  and  cat  passed  about 
10  cc  of  urine. 

June  6:  9  a.  m.,  found  dead. 
Cat  89.     White  and  black  female.     Weight,  2,860  grams.     Diet,  meat. 

June  5:  3.15  p.  m.,  28.6  cc  (0.2  gram  per  kilo)  of  2  per  cent  caffein  given  by  mouth 
through  stomach  tube,  no  vomiting  observed,  nor  any  other  symptoms;  3.30,  found 
dead.    Autopsy:  Organs  normal;  liver  congested. 


58 


THE   TOXICITY   OF   CAFPEIN". 


Cat  82.    Gray  female.     March  S,  weight  2,450  grams;  June  6,  weight  2,750  grams.    Diet, 
150  grams  of  vieat  daily. 

June  7 :  Giveu  0.4125  gram  of  caffein  in  150  grams  of  meat,  did  not  eat. 

June  8:  Given  0.4125  gram  of  caffein  in  150  grams  of  meat,  refused  to  eat. 

June  9:  Given  150  grams  of  meat  without  caffein,  ate  all  of  it. 

June  10:  No  food  given. 

June  11:  No  food  given. 

June  12:  Given  0.4125  gram  caffein  in  150  grams  of  meat  (150  mg  per  kilo),  ate  all 
of  it. 

June  13:  Found  dead.     Autopsy:  Lungs  congested,  liver  congested;  other  organs 
apparently  normal. 
Cat  100.    Gray  female.     Weight,  2,740  grams.    Diet,  vieat. 

July  17 :  3  p.  m. ,  17  cc  of  2  per  cent  cafiein  (124  mg  per  kUo)  given  by  mouth  through 
stomach  tube  at  3.20  p.  m. ;  5  p.  m.,  very  irritable,  but  no  other  symptoms. 

July  18:  Under  observation  all  day,  no  symptoms. 
Cat  93.    Black  and  white  female.     Weight,  1,640  grams. 

July  17:  3.30  p.  m.,  10  cc  (0.125  gram  per  kilo)  of  2  per  cent  caffein  given  by  mouth 
through  stomach  tube. 

July  18:  Under  observation  all  day,  no  symptoms. 

From  the  results  of  the  experiments  of  this  series  it  appears  that  0.15  gram\caffein 
per  kilo  may  be  fatal  within  a  few  hours  after  its  administration,  even  if  the  drug  is 
mixed  with  a  moderate  amount  of  meat.  Experiments  87  and  92  show,  however,  that 
this  amount  may  be  borne  by  some  individuals  without  any  serious  consequences,  as 
the  cats  were  under  observation  for  some  time  after  they  received  caffein,  and  no 
untoward  symptoms  were  noticed  in  either  of  them  during  this  time.  It  may  be 
remarked  that  cat  No.  92  vomited  shortly  after  it  received  caffein.  It  is  practically 
certain,  therefore,  that  this  amount  of  caffein  in  proportion  to  the  weight  of  the  animal 
will  in  the  great  majority  of  cases  prove  fatal,  and  perhaps  in  a  smaller  percentage  of 
individuals  it  is  surely  toxic  if  it  does  not  escape  absorption.  Smaller  doses  may 
cause  irritability  in  some  individuals,  but  symptoms  referable  to  nervous  symptoms 
of  muscles  were  absent,  as  in  experiments  Nos.  93  and  100.  The  minimum  fatal  dose 
of  caffein  for  the  cat  when  given  by  mouth  is,  therefore,  0.15  gram  per  kilo. 

Table  9. — Subcutaneous  injection;  cats. 

SERIES  A. 


Num- 
ber. 

Weight. 

Caflein 
per  kilo. 

Symptoms. 

Duration  of  life. 

4 

Grams. 
1,440 
1,396 

Gram. 
0.30 

.30 

65  minutes 

Over  29  hours. 

5 

About  2  hours. 

SERIES  B. 

3 

2,854 

0.25 

6 

1,645 

.243 

8 

1,735 

.25 

9 

1,900 

.25 

12 

1,185 

.20 

14 

1,8.55 

.20 

1.5 

2,145 

.20 

10 

1,100 

.236 

20 

790 

.25 

Few  minutes 

30  minutes 

1  hour 

3  hours 

1  hour  20  minutes 

40  miautes 

15  minutes 

SERIES  C. 


30  minutes. 

1  hour  30  minutes. 

1  hour. 

1  hour  45  miautes. 

Less  than  18  hours. 

Do. 

Do. 

Do. 
4  hours  30  minutes. 


24 

1,300 
2,  (;20 
1,045 
1,285 
2,285 

0. 153 
.15 
.15 
.155 
.14 

1  hour 

Survived. 

17 

15  m  inutes 

Do. 

23 

1  hour  10  minutes. 

7 

20  minutes 

1  hour. 

j9 

65  minutes. 

ACUTE  INTOXICATION — CATS. 


59 


Table  9. — Subcutaneous  injection;  cats — Continued. 
SERIES  D. 


Num. 
ber- 

Weight. 

Caffein 
per  kilo. 

Symptoms. 

Duration  of  life. 

13 

Orama. 
730 
1,165 
965 
1,605 
1,625 
2,335 
2,710 
1,785 
2,315 
2,325 

Oram. 
0.  i;w 

.138 
.103 
.125 
.125 
.128 
.129 
.123 
.112 
.120 

Restlessness 

21 

None 

25 

do 

26 

do 

27 

do 

28 

do 

40 

do 

Do. 

41 

do 

Do. 

42 

do 

Do. 

38 

Mild 

SERIES  E.i 


3,225 
3,050 
4,220 
4,250 


0. 124 
.118 
.084 
.084 


40  minutes. 
Died  soon  after. 
Survived. 
2  hours. 


Pathological  conditions.  *  Two  days  after  first  injection. 

Table  10. — Injections  into  peritoneal  cavity;  cats. 


Num- 
ber. 

Weight. 

Caffein 
per  kilo. 

Symptoms. 

Duration  of  life. 

99 

Qrams. 

3,000 

4,100 

1,450 

2,615 

505 

575 

860 

790 

2,970 

2,420 

Oram. 
0.100 
.100 
.137 
.145 
.200 
.139 
.200 
.200 
.200 
.183 

Mild 

Survived. 
Do. 
Do. 
Do. 

5  days. 

6  days. 

30  minutes. 
Survived. 
1  hour. 
30  minutes. 

98 

do.i 

93 

Very  mild 

87 

..do 

97 

None                            

96 

..do  .            

95 

15  minutes 

94 

10 

16 

1  In  few  minutes. 
Table  11. — Administration  of  caffein  by  mouth;  cats. 


No. 

Weight. 

Caffein 
per  kilo. 

Symptoms. 

Duration  of  life. 

91 

Qrams. 
3,050 
3,260 
1,750 
2,620 
2,685 
2,860 
2,450 
2,740 
1,640 

Oram. 
0.15 
.15 
.16 
.15 
.20 
.20 
.15 
.124 
.125 

1  hour  40  minutes 

2  hours. 

88 

1  hour  40  minutes. 

92 

2")  minutes 

Survived. 

87 

3  hours 

Do. 

90 

1  hoiu"  15  minutes 

Loss  than  18  hours. 

89 

75  minutes. 

82 

Less  than  24  hours. 

100 

1  hour  40  minutes 

Survived. 

93 

Do. 

SUMMARY. 


The  toxicity  of  caffein  in  cats  is  shown  to  be  the  same  when  given  by  mouth  as 
when  injected  subcutaneously,  the  minimum  fatal  doses  in  both  cases  being  0.15 
gram  per  kilo.  When  introduced  by  the  intraperitoneal  route,  caffein  is,  on  the 
contrary,  distinctly  less  toxic.    After  the  administration  of  0.137  and  0.145  gram 


60  THE   TOXICITY   OF   CAFFEIN". 

caffein  per  kilo  (Nos.  93  and  S7)  salivation  in  one  cat  (No.  93)  and  initability  and 
muscular  stiffness  in  the  other  were  the  only  effects  noticed.  These  symptoms  were 
no  longer  observed  the  next  day  and  the  cats  appeared  to  be  perfectly  normal.  Experi- 
ments vrith  larger  doses  indicate  that  the  minimum  fatal  dose  by  this  method  of 
administration  is  about  0.2  gram  per  kilo. 

EXPERIMENTS  ON  DOGS. 

The  experiments  were  carried  out  on  well-fed  adult  dogs  and  on  puppies,  kept 
imder  observation  for  some  time  before  the  drug  was  administered.  Only  those 
manifesting  no  signs  of  abnormality  were  used  for  these  tests.  Caffein  was  given  by 
mouth  mixed  with  10  to  20  grams  of  meat,  or  eubcutaneously  in  2  per  cent  aqueous 
solution.  The  young  animals  received  caffein  dissolved  in  milk.  The  determination 
of  the  minimum  toxic  or  fatal  doses  when  the  drug  was  fed  presented  considerable 
difficulty,  as  in  many  instances  the  ingestion  of  the  drug  was  closely  followed  by 
vomiting.  ,  > 

ADMINISTRATION  BY  MOUTH. 

«. 
Series  A. 

The  effective  dose  in  these  experiments  showed  considerable  variation.  One  dog 
(No.  38)  died  after  a  dose  of  0.12  gram  caffein  per  kilo,  while  some  subjects  survived 
doses  of  0.2  and  0.23  gram  per  kilo.  In  the  12  experiments  given  in  Table  12,  page  62, 
it  will  be  noticed  that  from  0.12  to  0.152  gram  per  kilo  proved  fatal  to  three  dogs, 
while  thi-ee  others  sm-\T.ved  the  same  amounts  in  proportion  to  the  body  weight.  The 
results  were  the  same  with  larger  doses.  It  may  be  observed  in  this  connection  that 
in  the  case  of  the  five  dogs  in  which  vomiting  was  noticed  some  time  during  the  24 
hotirs  following  the  administration  of  caffein,  four  suj-\dved.  No.  38  being  the  exception. 
The  greater  toxicity  of  caffein  in  this  case  is  in  all  probabihty  due  to  some  morbid 
process,  the  presence  of  which  was  indicated  by  the  high  temperature  of  this  subject. 

That  vomiting  may  avert  a  fatal  issue  after  larger  doses  of  caffein  is  made  fm-ther 
probable  by  experiment  on  dog  No.  48,  for  which,  in  the  absence  of  vomiting,  a  dose  of 
0.2  gram  of  caffein  per  kilo  proved  fatal.  On  this  supposition  the  discrepancy  in  the 
results  obtained  in  this  series  may  be  readily  explained.  The  smallest  doses  which 
proved  fatal  in  these  experiments  were  0.145  and  0.152  gram  per  kilo.  No.  38,  which 
died  from  a  dose  of  0.12gi-am  per  kilo,  may  be  considered  as  an  exception,  as  this  subject 
was  not  normal.  Experiments  with  caffein  on  dogs  were  made  at  various  other  times 
in  this  laboratory  but  failed  to  show  that  smaller  doses  of  caffein,  even  when  vomiting 
did  not  occur  after  its  administration,  were  fatal,  although  toxic  effects  were  observed. 
The  conclusion  is  therefore  justified  that  the  minimum  fatal  dose  of  caffein  for  the 
normal  dog  is  about  0.15  gram  per  kilo  when  given  by  mouth. 

subcutaneous  injection. 

Series  B. 

To  determine  the  toxicity  of  caffein  more  accurately,  especially  for  comparison 
with  animals  of  other  species,  the  subcutaneous  method  of  administration  was  also 
used.  The  injections  were  made  with  a  syringe  of  20  cc  capacity,  the  contents  of 
which  were  introduced  into  contiguous  areas.  The  results  of  experiments  on  six 
dogs  indicate  that  approximately  150  to  160  mg  per  kilo  is  the  minimum  fatal  dose, 
since  such  doses  proved  fatal  to  two  out  of  the  three  animals  receiving  this  amount, 
while  three  others  which  received  doses  of  from  143  to  160  mg  per  kilo  survived. 


ACUTE   INTOXICATION — DOGS.  61 

HXPBRIMENTS  ON  PUPPIES. 

Series  C. 

In  these  experiments  the  resistance  of  young  growing  puppies  to  caffein  was  studied. 
Caffein  waf<  given  by  mouth  to  all  the  subjects  except  one,  to  which  it  was  administered 
Bubcutancously.  The  protocols,  only  a  few  of  which  are  given,  and  the  tabulated 
data  of  the  experiments  (p.  62)  show  that  the  age  of  the  animal  has  a  decided 
influence  on  the  toxicity  of  caffein. 

Doa  11.     Weight,  1,260  grams. 

August  2:  At  10  a.  m.  given  12.5  cc  of  2  per  cent  of  caffein  through  stomach  tube; 
2  p.  m.,  had  con\'ulsions,  diarrhea,  salivation,  and  stiffness  of  limbs. 

August  3:  Found  dead  9  a.  m.  Autopsij:  Thoracic  \iscera  apparently  normal; 
stomach  immensely  distended  and  filled  with  a  white,  cheesy  ma.ss  and  some  fluid; 
round  worms  plentiful  in  stomach  and  small  intestine;  mucosa  of  entire  intestine 
congested;  contents  of  lower  intestine  congested;  liver  pale;  spleen  flabby;  kidney 
congested. 
Dog  10.     Weight,  1.650  grams. 

July  26:  9.30  a.  m.,  29  cc  of  2  per  cent  caffein  added  to  60 cc  of  milk  offered,  but 
refused,  and  was  therefore  fed  by  mouth  through  stomach  tube;  10.25  a.  m.,  no 
symptoms;  11.30  a.  m.,  restlessness,  extremities  stiff,  post,  extremities  spread  apart, 
dog  shows  well-marked  symptoms  of  caffein  poisoning;  12.10  p.  m.,  symptoms  more 
severe,  extremities  extended  and  spread  out,  is  hing  flat  on  belly  so  that  nose  touches 
floor  of  the  cage;  12.40  p.  m.,  found  dead;  was  alive  at  12.10  p.  m.  Autopsy:  Lungs 
showed  hemorrhagic  foci  in  all  lobes;  heart  apparently  normal;  liver  fatty;  stomach 
and  intestines  filled  with  roimd  worms;  spleen  and  kidney  apparently  normal. 
Dog  9.     Weight,  S,000  grams. 

July  25:  350  mg  caffein  per  kilo;  5  p.m.,  lying  down  most  of  the  time,  occasionally 
walks  about  in  stall;  restlessness  present,  but  not  marked;  5.30  p.  m.,  vomit  which 
looked  frothy  and  mucilaginous  noticed  on  the  floor  of  the  stal';  no  meat  particles 
noticed  in  vomit,  though  seiirched  for;  whines  occasionally. 

July  26:  9  a.  m.,  looks  well;  no  signs  of  the  effect  of  caffein  given  the  day  previous. 
Dog  S.     YeUow  female.     Weight,  3,100  grams. 

July  22:  10.50  a.  m.,  received  1.1  grams  of  caffein  in  10  grams  of  meat  (354  mg  caffein 
per  kilo);  3  p.  m.,  vomited  mucus;  gait  clumsy;  refused  to  eat;  continually  drinking 
water;  vor>'  restless;  4  p.  m.,  conv-ulsions  set  in  at  3.55  p.  m.;  tonic  rigidity  of  the 
posterior  extremities;  profuse  salivation;  conxnilsions  were  both  tonic  and  clonic  in 
character,  and  resembled  those  seen  in  rabbits  in  caff'ein  intoxication;  a  striking 
feature  was  the  duration  of  the  spasm,  which  began  at  3.55  p.  m.  and  kept  up  for  more 
than  two  hours. 

July  23:  Found  dead  at  9  a.  m. 

The  data  recorded  in  the  table  and  in  the  protocols  of  the  experiments  of  series  C 
show  that  four  out  of  the  seven  animals  experimented  upon  died  in  less  than  24  hours 
after  caffein  was  fed ;  three  of  these  received  300  to  354  mg  caffein  per  kilo,  and  one 
received  200  mg  caft'ein  per  kilo.  No.  8  vomited  four  hours  after  caffein  was  given. 
No  vomiting  was  obser\-ed  in  the  other  three  dogs.  From  0.300  to  0.350  gram  of 
caffein  per  kilo  may  be  regarded,  therefore,  as  surely  fatal  to  young  gi-owing  puppies. 
That  this  is  in  all  probability  the  minimum  lethal  dose  appears  from  the  following 
experiments:  No.  9,  which  received  350  mg  per  kilo,  vomited  one  hour  after  and 
survived,  which  indicates  that  some  of  it  was  probably  not  absorbed.  The  amount 
which  entered  the  circulation  was  therefore  less  than  350  mg  per  kilo.  Since  No.  15, 
which  received  250  mg  caffein  subcutaneously,  likewise  survived,  the  probabilities 
are  that  300  to  350  mg  per  kilo  were  the  minimum  fatal  doses  for  these  animals.  More- 
over, No.  12,  which  received  200  mg  caffein  per  kilo,  sur\'ived,  no  vomiting  ha\'ing 
been  obsers'ed.  The  case  of  No.  11,  in  which  the  same  amount  of  caffein  in  proportion 
to  body  weight  proved  fatal,  may  be  explained  perhaps  by  the  findings  of  the  autopsy. 

The  results  obtained  in  these  experiments  justify  the  conclusion  that  young  growing 
dogs  can  stand  larger  doses  of  caffein  than  full-grown  and  older  dogs. 

Attention  may  also  be  called  here  to  the  difference  in  the  sjTnptom?  produced  by 
caffein  in  very  young  and  in  adult  dogs.    It  was  often  noticed  in  these  experimenta 


62 


THE   TOXICITY   OF   CAPFEIN". 


that  the  symptoms  in  older  subjects  when  given  toxic  doses  of  caffein  set  in  rather 
abruptly  and  ended  in  instantaneous  death.  We  failed  to  observe  this  phenomenon 
after  the  administration  of  large  amounts  of  caffein  to  very  young  dogs,  in  which  tonic 
and  clonic  convulsions  alternating  with  paresis  were  observed.  These  symptoms  set 
in  rather  gradually  and  lasted  several  hours  (see  experiment  No.  8),  resembling  the 
rabbit  in  this  regard. 

SUMMARY. 

The  toxicity  of  caffein  for  adult  dogs  is  about  the  same,  whether  given  by  mouth 
or  injected  subcutaneously.  The  resistance  of  puppies  to  caffein  is  much  greater  than 
that  of  adults. 

Table  12. — Administration  by  mouth;  dogs.     {Series  A.) 


No. 

Weight. 

Caffein 
per  kilo. 

Results. 

Remarks. 

47 

Kilos. 
13.60 
12.75 
7.95 
13.60 
6.50 

23.10 

11.50 
12.00 

13.40 
13.15 
14.50 

10.30 

Gram. 
0.144 
.200 
.200 
.147 
.230 

.120 

.174 
.200 

.200 
.152 
.120 

.145 

Vomiting  observed. 

"15 

do 

Stiffness  of  muscles;  no  other  symptoms. 

56 
52 

Found  dead  next  day. . 
Survived 

57 

do 

Vomited  after  1  hour;  convulsions  after  1  hour  and  45 

39 

....do 

minutes. 
Increased  frequency  of  respiration,  thirst,  loss  of  appe- 

48 

do 

tite,  vomited  rest  of  day  when  he  drank  water,  sali- 
vation, restlessness,  passed  feces  frequently. 
Vomiting  observed. 

48 
54 

Found  dead  next  day. . 

No  vomiting  observed.    Second  dose  was  given  8  days 

after  first. 
Vomiting  observed. 

Symptoms  after  1§  hours:  Dog  had  a  temperature  of 

49 
3S 

Foxmd  dead  next  day. . 
do 

IS 

.do 

104°  F.  before  caffein  was  given;  vomited  3  hours 
after  caffein  was  fed. 

Table  13. — Subcutaneous  injection;  dogs.      (Series  B.) 


No. 

Weight. 

Caffein 
per  kilo. 

Results. 

Remarks. 

62 

Kilos. 

9.30 
14.00 
12.00 
14.00 

7.20 

14.60 

Gram. 
0.161 
.160 
.1.50 
.150 
.160 

.143 

Survived 

Restlessness  and  vomiting  one-half  hour  after  injection. 

61A 
63 

Found  dead  next  day. . 
Survived 

Restlessness  1  hour  after  injection. 

64 

do 

Restlessness  and  thirst  45  minutes  after  injection. 

59 
61 

Died  1  hour  and  20 
minutes  after  injec- 
tion. 

Marked  restlessness,  but  no  convulsion. 
Symptoms  observed  in  li  hours. 

Table  14. — Administration  by  mouth  to  puppies.     (Series  C.) 


No. 

Weight. 

Caffein 
per  kilo. 

Result. 

Remarks. 

8 
9 

Kilos. 
3.10 

3.15 

1.60 
1.26 
1.28 
1.20 
3.50 

Gram. 
0.354 

.3.50 

.350 
.200 
.200 
.250 
.300 

Found  dead  ncXt  day . 
Survived    

Vomited  in  4  hours  after  feeding;  restlessness,  loss  of 
appetite,  thirst,  incoordination  of  muscles,  con%nil- 
sions. 

Muscular  incoordination   and   stiffness,   restlessness, 

10 
11 

Died  in  3  hours 

Found  dead  next  day . 
Sunnved 

vomited  1  hour  after  caffein  was  given. 
Convulsion;  no  vomiting. 
Salivation;  convulsions. 
No  svmptoms. 

15 
10 

do........ 

Died  in  1  hour 

Subcutaneous  injection. 

Convulsions  45  minutes  after  caffein  was  fed. 

CHRONIC   INTOXICATION — RABBITS.  63 

CHRONIC  CAFFEIN  INTOXICATION. 

The  object  of  tliis  study  was  to  ascertain  the  effect  of  repeated 
dosage  when  caffein  was  given  daily  or  at  longer  intervals.  The 
experiments  were  tried  on  rabbits  and  on  dogs.  As  in  the  experi- 
ments on  acute  intoxication,  the  animals  were  under  observation  for 
some  time  in  the  laboratory  before  the  administration  of  caffein 
was  begun  in  order  to  ascertain  the  presence  or  absence  of  abnor- 
mality. The  relation  of  diet  to  toxicity  received  some  attention, 
but  the  question  was  not  studied  exliaustively  in  the  present  inves- 
tigation. 

EXPERIMENTS  ON  RABBITS. 

Full-grown  adult  as  well  aa  young  rabbits  were  employed.  The  diet  consisted 
either  of  carrots  or  of  oats;  water  was  given  ad  libitum.  The  rabbits  were  kept  in 
metal  cages  in  a  well-lighted  and  well-ventilated  room.  Unnecessary  handling  or 
any  other  procedure  tending  to  fatigue  or  to  cause  discomfort  to  the  animals  was 
very  carefully  avoided,  since  we  had  found  that  such  treatment  was  likely  to  decrease 
the  resistance  of  the  rabbit  to  caffein.  The  caffein  was  administered  by  feeding  by 
mouth  and  through  a  stomach  tube,  or  by  the  subcutaneous  method.  In  a  good  many 
cases  it  was  given  daily,  in  some  at  longer  intervals. 

Series  A. 

The  experiments  of  this  series  formed  a  preliminary  study  for  the  purpose  of  testing 
the  effect  of  moderate  doses.  One  decigram  of  caffein  per  kilo  was  given  daily  for 
several  days;  when  administered  at  longer  intervals  the  dose  was  increased  to  150  to 
200  mg  per  kilo.  It  was  found  that  the  smaller  doses  did  not  produce  any  symptoms; 
even  the  weights  of  the  animals  were  not  influenced.  Doses  of  medium  size  given  on 
two  successive  days  were  likewise  without  any  noticeable  effect  (Nos.  182,  183,  123, 
101).  When  a  third  dose  of  this  size  was  given  within  48  or  24  hours  it  proved  fatal 
(Nos.  123, 182,  and  183).  Exceptionally,  however,  moderately  large  doses  (for  rabbits) 
may  be  given  for  three  consecutive  days  without  fatal  issue,  as  in  rabbit  No.  101. 
When  given  at  intervals  of  two  to  three  days,  larger  doses,  as  may  be  seen  from  the 
protocols,  can  be  administered  without  causing  acute  death  (Nos.  173,  181,  201). 

The  results  of  the  tests  of  this  series  point  to  the  absence  of  any  accumulation  and 
to  the  possible  elimination  of  moderate  doses  of  caffein  and  its  products  of  decom- 
position within  24  hours  or  thereabouts.  'WTien  the  doses  are  larger  the  time  of  its 
elimination  is  apparently  longer,  as  shown  by  the  fact  that  repetitions  of  the  dose  the 
next  day  may  be  fatal,  but  when  a  longer  interval  is  allowed  it  may  be  given  without 
causing  death.  It  will  be  observed  that  only  one  rabbit  of  this  series  8ur\-ived,  but 
it  was  extremely  emaciated.  This  condition  has  been  observed  in  a  number  of  cases 
after  caffein  had  been  given  for  several  days.  Even  when  the  drug  was  Avithdrawn 
the  animals  continued  to  lose  weight.  This  may  be  explained  by  the  condition  of 
the  gastro-intestinal  canal  as  found  at  autopsy.  The  presence  of  inflammation  of  the 
mucous  membrane  of  the  stomach  and  intestines,  with  ulceration  of  the  mucous  mem- 
brane of  the  pylorus  in  one  of  the  rabbits  (No.  173)  of  the  series,  in  all  probability 
caused  diminution  or  loss  of  appetite,  which  of  itself  would  tend  to  cause  loss  of  flesh 
and  strength  and  finally  death.     Protocols  of  the  experiments  follow. 


64 


THE   TOXICITY   OF   CAFFEIN. 


Rabbit  173.     Carrots  ivere  fed  from  October  1  to  18  and  oats  for  the  remainder  of  the  experi-     ' 
ment. 


Date. 

Weight. 

Caflein 
per  kilo. 

Date. 

Weight. 

Caffein 
per  kilo. 

Oct.  9 

Grams. 
1,980 
1.905 
1,930 

Oram. 
0.141 
.190 
.207 

Oct.  16 

Grams. 
2,005 
1,845 
1,740 

Gram. 
0.220 

Oct.  11 

Oct.  18 

Oct.  13 

Oct.  20             .  . 

230 

October  21:  Paralysis  of  posterior  extremities. 

October  22:  9  a.  m.,  found  dead. 

The  urine  was  examined  before  and  after  the  administration  of  caffein.  No  symp- 
toms were  observed  after  the  administration  of  caffein  (5  doses  in  11  days),  nor  was 
albumen  or  sugar  found  in  the  urine  after  any  of  the  experiments  on  this  rabbit. 
Autoj}sy:  Pyloric  mucosa  exhibited  several  ulcers;  small  intestines  showed  slight 
inflammation;  liver  deeply  congested;  kidneys  showed  marked  inflammation  of  cortex; 
other  organs  practically  normal. 

Rabbit  181.     Diet,  carrots  September  29-October  17,  then  oats. 


Date. 

Weight. 

Cafieln 
per  kilo. 

Date. 

Weight. 

Caffein 
per  kilo. 

Oct.  4 

Grams. 
1,425 
1,450 
1,270 
1,210 
1,375 
1,305 

Gram. 
0.105 
.100 
.100 
.100 
.130 
.153 

Oct.  11 

Grams. 
1,370 
1,385 
1,345 
1,030 
1,230 
1,215 

Gram. 
0  175 

Oct.  5 

Oct.  13 

.180 

Oct.  6 

Oct.  16      

200 

Oct.  7 

1  Oct.  17 

Oct.  8 

Oct.  18 

Oct.  9 

Oct.  20 



Rabbit  was  markedly  emaciated  and  weak, 
urine  as  a  result  of  caffein  feeding. 

Rabbit  182.     Diet  of  carrots  from  September  29. 
Received  caffein  subcutaneously  as  follows: 


No  albumen  or  sugar  found  in  the 


Date. 

Weight. 

Caffein 
per  kUo. 

Date. 

Weight. 

Caffein 
per  kilo. 

Oct.  4 

Grams. 
1,765 
1,880 
1,750 

Gram. 
0.100 
.100 

.100 

Oct.  8           

Grams. 
1,685 

Gram. 
.135 

Oct.  5 

Oct.  9  

.150 

Oct.  6 

Oct.  11 

1,605 

.174 

Oct.  7 

1,710              -100 

October  12:  11  a.  m.,  23  hom's  after  caffein  was  given,  convulsions  with  recovery; 
rabbit  died  at  1.30  p.  m.  No  sugar  was  found  in  the  urine  at  any  time  after  the 
administration  of  caffein.     Albumen  was  present  only  in  one  specimen. 

Rabbit  183.     Diet  of  carrots  from  September  29. 
Received  caffein  subcutaneously  as  follows: 


Date. 

Weight. 

Caffein 
per  kilo. 

Date. 

Weight. 

Caflein 
per  kilo. 

Oct. 4 

Grams. 
1,.385 
1,400 
1,385 
1,240 

Gram. 

0.100 

.100 

.100 

.122 

Oct.  8        

Grams. 
1,310 
1,390 
1,390 

Oram. 
0.153 

Oct.  5 

Oct  9                       ...          

.142 

Oct.  6 

Oct.  11              

.187 

Oct.  7 

October  12:  9  a.  m.,  found  dead, 
sample  contained  sugar. 


No  albumen  was  found  in  the  urine.     Only  one 


CHRONIC   INTOXICATION RABBITS. 


65 


Rabbit  12.3.     ^Vh^te,  female.     Diet,   oats. 

Received  caffein  subcutaneously  as  follow.s: 


Date. 


Apr.  14 
Apr.  16 
Apr.  17 


Weight. 


Orams. 
2,350 
2,250 
2,325 


Caffein 
per  kilo. 


Grams. 
42 
90 
80 


Date. 


Apr.  20 
Apr.  21 
Apr.  22 


Weight. 


Grams. 
2,126 
1,965 
1,876 


Caflein 
per  kilo. 


Orams. 
141 
152 
160 


Rabbit  died  30  minutes  after  last  injection  of  caffein.  Autopsy:  Stomach  exhibited 
marked  inflammation  of  mucosa.  Slight  enteritis.  Liver  and  kidneys  were  deeply 
congested  and  dark  colored. 

Rabbit  No.  101,  white  male.    Diet,  oats. 
Received  caffein  subcutaneously  as  follows: 


Date. 

Weight. 

Caffein 
per  kilo. 

Date. 

Weight. 

Caffein 
per  kilo. 

Mar.  IS                      

Grams. 
2,025 
1,970 
2,009 
1,855 
1,738 

Gram. 
0.100 
.100 
.100 
.100 
.114 

Mar.  24 

Grams. 
1,815 
1,830 
1,710 
1,734 
1,000 

Gram. 
0.166 

Mar.  19                     

Mar.  25 

.185 

Mar.  20    

Mar.  26 

.176 

Mar.  22 

Mar.  29 

.219 

Mar.  23 

Apr.  1 

.224 

April  5:  Found  dead.  Autopsy:  Marked  inflammation  of  gastric  mucosa.  Con- 
siderable enteritis  affecting  the  whole  extent  of  the  intestines;  liver  congested  and 
friable;  kidneys  deeply  congested  in  cortical  and  medullary  portions;  spleen  con- 
gested, but  of  normal  size;  lungs  and  heart  normal. 

Four  days,  0.1  per  kilo;  10  doses  in  14  days. 
Rabbit  201.    Diet  of  carrots  begun  October  1;  October  19,  oats. 

Subcutaneous  injections  as  follows: 


Date. 

Weight. 

Caffein 
per  kilo. 

Date. 

Weight. 

Caflein 
per  kilo. 

Oct.  9 

Orams. 

1,000 

1,015 

1,005 

Gram. 
0. 150 

.  ISO 
.187 

Oct.  16 

Grami. 

1,005 

850 

890 

Gram. 
0.225 

Oct.  11... 
Oct.  13... 

Oct.  IS.. 
Oct.  20.. 

.111 

Under  observation  six  hours  October  20;  no  symptoms. 

October  23:  Died;  was  much  emaciated  but  did  not  show  any  sjinptoms;  emaciation 
set  in  when  caffein  was  withdrawn;  urine  never  contained  sugar  or  albumen;  symp- 
toms observed  after  second  dose  only. 

Series  B. 

The  question  whether  caffein  is  cumulative  in  the  rabbit,  suggested  in  the  preceding 
experiments,  was  the  subject  of  further  investigation  in  Series  B.  Caffein  was  given 
by  mouth  or  subcutaneously.  Carrots  formed  the  exclusive  diet,  a  measured  amount 
being  given.  The  rabbits  were  kept  under  observation  for  two  weeks,  except 
Nos.  370  and  373,  records  of  which  were  made  only  for  four  days  before  the  administra- 
tion of  caffein  was  begun.  Caffein  was  given  by  mouth  in  experiments  of  Groups  I 
and  III.  Rabbits  292,  293,  and  29-5  received  daily  20  cc  water  by  mouth  for  four  days 
previous  to  the  administration  of  caffein,  while  in  the  rabbits  of  Group  II  the  caffein 
treatment  was  preceded  by  the  injection  of  0.8  per  cent  salt  solution  subcutaneously. 
The  object  in  both  cases  was  to  ascertain  whether  or  not  the  method  of  the  adminis- 
tration of  caffein  has  any  influence  on  the  animal,  but  observation  made  from  day  to 
18594°— Bull.  148—12 5 


66  THE   TOXICITY   OF    CAFFEI:N-. 

day  failed  to  show  any  effect  of  such  treatment.  About  1  decigram  of  caffein  per 
kilo  was  administered  daily,  with  occasional  intermissions.  Later  in  the  com'se  of 
the  experiment  the  doses  were  increased,  0.15  gram  per  kilo  being  the  maximum  dose 
given.  Rabbit  293  died  after  the  third  dose  with  symptoms  of  typical  caffein  poison- 
ing. The  administration  of  the  same  dose  of  caffein  was  continued  10  days  longer  in 
Nos.  292  and  295.  It  was  omitted  on  the  seventh,  fourteenth,  and  fifteenth  days  of 
the  experiment.  On  the  eighteenth  day  of  the  experiment  the  dose  was  increased  to 
150  mg  per  kilo  and  was  repeated  2  days  later.  No.  295  was  found  dead  the  next 
day.  No.  292  survived.  Rabbits  313  and  315  may  be  considered  together,  as  they 
were  treated  alike  in  every  respect.  The  initial  dose  of  100  mg  caffein  per  kilo  was 
finally  increased  to  122  mg.  After  the  twelfth  dose  the  emaciation  was  well  marked 
and  the  rabbits  were  very  weak.  No.  313  was  found  dead  2  days,  and  No.  315 
3  days,  after  the  last  dose  of  caffein  was  given.  It  should  be  remarked  in  this  con- 
nection that  symptoms  of  caffein  poisoning  were  never  observed  in  these  rabbits. 
Death  was  not  due,  therefore,  primarily  to  caffein,  but  the  rapid  loss  of  flesh  and 
strength  observed  during  the  last  few  days  suggests  that  it  was  due  to  malnutrition 
apparently  brought  about  by  caffein. 

The  results  obtained  by  subcutaneous  injection  of  caffein  are  given  in  the  table 
as  Group  II.  The  initial  dose  of  100  mg  per  kilo  was  injected  daily.  No.  298  died 
after  the  second  dose.  Nos.  223  and  296  received  this  amount  daily  for  6  days. 
An  intermission  of  2  days  followed,  at  the  end  of  which  the  same  dose  was  given 
again.  The  next  day  it  was  increased  to  150  mg  per  kilo,  but  no  effect  was  observed ; 
48  hours  later  this  dose  was  repeated.  No.  223  was  found  dead,  but  its  mate  survived. 
Symptoms  of  acute  caffein  intoxication  were  not  observed  in  any  of  these  rabbits. 
It  would  seem,  therefore,  that  caffein  is  not  cumulative.  This  supposition,  however, 
appears  somewhat  contradictory  in  view  of  the  fact  that  out  of  the  eight  rabbits  of 
this  series  six  died,  nor  could  any  cause  of  death  be  ascribed  other  than  caffein.  Also 
the  first  results  of  Experiments  293,  370,  and  373  might  be  considered  as  indicat- 
ing that  cumulation,  though  to  a  moderate  extent,  does  take  place,  since  in  these 
cases  reflexes  developed  after  the  drug  was  given  for  some  time.  But  this  view  is 
contradicted  by  the  results  of  Experiment  371,  in  which  150  mg  per  kilo  given  5 
days  after  the  daily  dosage  of  caffein  was  suspended  likewise  caused  increased  reflexes. 
Cumulation,  therefore,  does  not  account  for  the  effects  noted  in  the  other  rabbit.  It 
will  be  observed  that  rabbit  No.  370,  as  well  as  Nos.  371  and  373,  had  diarrhea  for 
several  days.  It  is  quite  possible  that  the  weakened  condition  rendered  the  rabbits 
more  sensitive  to  the  action  of  the  drug.  This  is  made  highly  probable  by  the  obser- 
vations recorded  in  the  experiments  on  acute  intoxication  with  caffein  in  which 
death  occurred  after  small  doses.  In  such  cases  some  pathological  condition  was 
often  disclosed  by  the  autopsy.  The  results  of  this  series  corroborate,  therefore,  those 
of  Series  A,  and  indicate  again  the  absence  of  cumulative  action.  The  results  ob- 
tained are  in  all  probability  due  to  malnutrition  and  other  conditions  brought  about 
by  congestion  of  the  viscera  and  consequent  injury  to  the  gastro-intestinal  canal. 


CHRONIC    INTOXICATION RABBITS.  67 

Table  16. — Chronic  caffcin  intoxication  of  rabbits;  Series  B  on  cumulation. 


i 

1               ( 

^roup  1. 

1 

Group  II, 

Group 

III. 

Data. 

1 

1 

1 

No.  292. 

No.  293. 

No.  295. 

No.  296. 

No.  223. 

No.  298. 

No.  315. 

No.  313. 

Diet  (grams  carrots  in  2  days) 

;     1,000 

1,000 

975 

930 

905 

880 

355 

300 

f'afTein  administered  (cc)  and  weight 

1 

Lrrams): 

( 

1 

Mar.5 

I  i,4i6 
/   • 

1,470 

1,015 

1,040 

1,070 

955 

770 

770 

Mar.  7 

\  1,415 
/ 

1,3G0 

1,140 

1,090 

1,095 

1,000 

715 

690 

Mar.O 

■  \  1,350 

1,270 

1,070 

1,000 

1,055 

1,005 

655 

665 

Mar.  11 

■{  i.sos 

f 

1,465 

1,190 

1,230 

1,285 

1,250 

755 

760 

Mar.  10 

■\  i,580 
/      -   •■ 

1,460 

1,230 

1,165 

1,170 

1,145 

730 

745 

Mar.  17 

■\  1,515 

1,415 

1,080 

1,040 

1,115 

1,105 

720 

685 

Mar.  19 

■\  1,565 

1,570 

1.280 

1,195 

1,235 

1,220 

710 

7:« 

•{  1.585 

7 
1,530 

6 
1,265 

4 
755 

4 

Mar.21 

1,150 

1,215 

1.260 

700 

-{  1.440 

7 

6 

(') 

(') 

(') 

4 

4 

Mar.  22 

1,315 

1,175 

1,100 

1.045 

1,150 

675 

635 

■{  1,335 

7 

G 

(') 

(') 

(') 

4 

4 

1,140 

1.110 

1,145 

1.190 

1,230 

715 

700 

•{  1.310 

6 

(') 

(') 

(') 

4 

4 

Mar.  24 

(-) 

1,090 

1,115 

1,170 

1,250 

680 

650 

Mar.2o 

•  {  1,375 
{  1,255 

6 
1,035 

6 
1,095 

(') 
1,125 

/,2\5 

(•) 
1,215 

4 
695 

4 
675 

4 
685 

Mar.  26 

1,105 

1,155 

1,150 

695 

Mar.27 

•{ 

:} r 

6 

5.5 

6 

6 

4 

4 

Mar.  28 

■  \  1,.355 

1,115 

1,120 

1,160 

1,155 

595 

685 

•{  1,385 



6 

6 

6 

5 

4 

4 

Mar.  29 

1.150 

1,155 

1,165 

955 

695 

675 

Mar.30 

•,{  1,330 

6 
1,075 

6 
1.035 

6 
1,095 

Dead.' 

4 

630 

4 
610 

Mar.31 

IV  1,325 

6 
1,170 

6 
1,110 

6 
1,140 

4 
690 

4 
605 

Apr.l 

-{  1,335 

6 
1,050 

6 
1,050 

6 
1,120 

4 

625 

4 
620 

Apr.  2 

•;{  1,390 

6 
1,125 

6 
1,090 

6 
1,155 

4 
695 

4 

625 

Apr.  3 

■{ 

200 

1 

Apr.  4 

■  \  i.3(KJ 

1,005 

1,105 

1,080 

68.5 

580 

Apr.  5 

■{  1.3S5 

i          ^ 
\  1.-260 
r 

;::.:::: 

0 

1,090 

7.5 

1,010 

6 

1,130 

7.5 

1.050 

6 
1,090 

8 
1,110 

4 
655 

4 

630 

Apr.  6 

560 

530 

Apr.7 

•{ 

(0 

■\  1,260 

7.5 
1,000 

7.5 
1,090 

8 
1,065 

Apr.  8 

Dead. 

.\pr.  9 

Dead 

Sur- 

Dead. 

Dead. 

vived. 

1 

vived. 

1  On  these  davs  5  cc  of  salt  solution  was  administered  subcutaneously. 

2  Dead  Mar.  23. 

'  Found  dead  9  a.  m. 


68 


THE   TOXICITY   OF   CAFFEIN". 


Table  17. — Chronic  intoxication  of  rabbits,  series  B,  Group  IV,  on  cumulation. 

RABBIT,  370. 


Date. 

Weight. 

Carrots. 

Water. 

Uriiie. 

Caffeln 

by 
stomach. 

Symptoms. 

Aug  7          

Grams. 
2,155 
2,030 
2,105 
2,095 
2,105 
2,125 
2,120 
2,170 
2,175 
2,170 
2,175 
2,095 
2,120 
2,120 
2,120 
2,040 
2,030 
1,950 
1,885 

Grams. 
450 
450 
290 
450 
450 
450 
350 
450 
350 
360 
310 
180 
400 
400 
400 
400 
370 
215 
195 

cc. 
50 
25 
0 
30 
65 
65 
25 
35 

(?) 
65 
35 
40 

(?) 

45 
35 
40 
35 

280 
185 
275 
335 
360 
220 
265 
275 
200 
250 
170 
285 
285 
310 
250 
265 
220 
120 
60 

Mg  per 

kilo. 

Aug.  8          

Aug  9 

Aug  10 

Aug.  11 

50 
50 
50 
75 
75 
75 
100 
100 
125 
125 
125 
150 
150 
150 
200 

Aug.  12 

Aug.  13 

Aug.  14 

Aug.  15 

Aug.  16 

Aug.  17 

Aug.  18 

Severe  diarrhea. 

Aug.  19 

Do. 

Aug.  20 

Better. 

Aug.  21 

Do. 

Aug.  22 

Diarrhea  bad. 

Aug.  23 

Diarrhea  better. 

Aug.  24 

Do. 

Aug.  25             

Reflexes. 

Aug.  26 

Found  dead  at  9. 

RABBIT,  373. 


Aug.  7. 
Aug.  8. 
Aug.  9. , 
Aug.  10. 
Aug.  11. 
Aug.  12 
Aug.  13 
Aug.  14 
Aug.  15. 
Aug.  16 
Aug.  17 
Aug.  18 
Aug.  19 
Aug.  20 
Aug.  21 
Aug.  22 
Aug.  23 
Aug.  24 
Aug.  25 
Aug.  2G 
Aug.  27 
Aug.  28 
Aug.  29 

Aug.  30 
Aug.  31 


2,240 
2,150 
2,120 

450 
150 
205 

50 

30 

0 

230 
300 
150 

2,150 
2,195 

450 
450 

15 
5 

245 
285 

50 

2,160 

450 

65 

325 

50 

2,120 

300 

45 

190 

50 

2,195 

450 

40 

265 

75 

2,215 

350 

35 

200 

75 

2,205 

310 

45 

225 

75 

2,240 

400 

40 

265 

100 

2,255 

350 

30 

320 

100 

2,115 

185 

(?) 

170 

125 

2,115 

280 

35 

195 

125 

2,050 

175 

75 

115 

125 

2,060 

180 

75 

130 

150 

2,005 

200 

75 

125 

150 

1,990 

200 

75 

150 

150 

1,950 

255 

55 

132 

175 

1,870 

205 

80 

140 

None 

1,830 

200 

50 

140 

...do 

1,950 

400 

25 

265 

...do 

1,825 

400 

0 

315 

...do 

1,850 

10 

140 

...do 

1,835 

Severe  diarrhea. 
Diarrhea  better. 
Slight  diarrhea. 

Reflexes. 
Slight  diarrhea. 
Severe  diarrhea. 

Do. 

Do. 
Slight  diarrhea. 

Very  weak  and  in  poor  condi- 
tion. 


CHRONIC   INTOXICATION — RABBITS. 


69 


Table  17. — Chronic  intoxication  of  rabbits,  series  B,  Group  IV,  on  cumulation — Contd. 

RABBIT,  371. 


Date. 

Weight. 

Carrots. 

Water. 

Urine. 

Cadcin. 

Symptoms. 

.\ug.  7 

Orams. 
2.240 
2.2l« 
2.310 
2.295 
2. 320 
2. 280 
2.300 
2.205 
2,200 
2,295 
2.180 
2,150 
2,075 
2,075 
2.105 
2.105 
2.080 
2,105 
2.055 
2.040 

Orams. 
450 
450 
430 
450 
450 
450 
350 
425 
250 
155 
105 
125 
210 
280 
200 
400 
300 
250 
320 
190 

cc. 
50 
50 

(?) 
50 
50 
70 
70 
55 
40 
70 
70 
70 

(?) 
70 
50 
50 
0 
15 
10 
75 

300 
225 
300 
305 
335 
400 
255 
154 
125 

Lost 

120 
100 
192 
180 
225 
275 
145 
245 
176 
250 

Mg  per 
Kilo. 

Aug.  8 

Aug.  9 

Aug.  10 

Aug.  11 

50 

60 

50 

75 

75 

75 

100 

100 

100 

100 

None 

...do 

Aug.  12 

Aug.  13 

Aug.  14 

Aug.  15 

Aug.  10 

Aug.  17 

Aug.  18 

Aug.  19 

Diarrhea  severe. 

Aug.  20 

Do. 

Aug.  21 

Aug.  22 

Aug.  23 

do             Di.irrhea  spverfi. 

Aug.  24 

...do 

150 
150 

Do. 

Aug.  25 

RcQexes. 

Aug.  20 

Died  at  1  p.  m.,  without  having 
showed  any  symptoms  other 
than  reflexes. 

Series  C. 

The  subjects  used  in  these  experiments  were  rabbits  of  medium  size  and  were  appar- 
ently young  or  at  any  rate  were  not  very  old.  The  series  was  planned  for  the  study 
of  the  possible  effect  of  diet  on  the  toxicity  of  caffein  when  given  for  some  time,  and 
therefore  oats  were  substituted  for  carrots,  which  had  been  fed  in  the  previous  work,  as 
already  stated.  Caffein  was  given  by  mouth  in  the  usual  way,  in  1  per  cent  solution, 
100  mg.  per  kilo  daily.  Fourteen  rabbits  were  used  for  these  tests.  Their  weights  were 
recorded  daily  and  observations  made  at  frequent  intervals  during  the  day. 

The  only  change  noticed  in  all  of  the  experiments  of  this  series  was  progressive  loss 
of  weight  which  set  in  from  3  to  8  days  after  the  administration  of  the  drug  was  begun. 
The  duration  of  life  varied  considerably.  No.  382  died  after  the  fiiJi"st  dose.  No.  389 
lived  2  days.  No.  386,  3  days,  and  No.  385,  5  days,  No,  390  lived  7  days  and  No.  404 
lived  20  days  after  the  administration  of  caffein  was  begun.  The  duration  of  life  in  all 
the  others  was  from  11  to  16  days.  The  findings  at  autopsy  are  interesting  and  suggestive 
as  regards  the  possible  explanation  of  the  effects  of  repeated  dosage  of  caffein .  In  eight 
of  the  rabbits  there  was  involvement  of  (he  mucous  membrane  of  the  stomach  or  intes- 
tines or  of  both.  Since  the  same  condition  of  the  gastro-iutestinal  canal  was  observed 
in  previous  experiments  with  caffein  when  injected  subcutaneously,  the  mere  passing 
of  the  tube  into  the  stomach  is  obv-iously  not  the  cause  of  this  condition.  The  fatal 
outcome  due  is  therefore,  as  was  suggested  above,  to  inanition  brought  about  by  the 
condition  of  the  gastro-intestinal  canal.  Moreover  parallel  experiments  carried  out 
on  rabbits  in  the  same  way  with  alcohol  8ur\dved  this  treatment  much  longer. 
Obviously  then  the  passing  of  the  soft  rubber  catheter  is  not  the  cause  of  this  condition 
of  the  gastro-intestinal  canal  nor  the  diet.  Rabbits  were  fed  oats  exclusively  for  several 
months  in  this  laboratory'  and  thrived.  The  presence  of  pneumonia  in  the  other 
rabbits  of  this  series  may  be  regarded  as  accidental,  as  it  is  inconceivable  that  one  or 
two  doses  of  caffein,  as  was  the  case  in  Nos.  382  and  389,  could  predispose  the  lungs  to 
infection.  The  results  of  these  experiments  therefore  are  in  hai'mony  with  those  of 
the  preceding  two  series,  indicating  that  caffein  does  not  accumulate  in  the  body ,  and 
that  the  toxicity  of  caffein,  whether  of  the  single  dose  or  of  repeated  doses  is  the  same, 


70 


THE    TOXICITY    OF    CAFFEIN. 


on  a  diet  of  carrots  or  of  oats.  These  results  also  show  that  caffein  is  much  more  toxic 
with  repeated  dosage.  As  stated  in  the  historical  part  of  this  bulletin  the  same  view 
was  held  by  Gourewitch.^^ 

Rabbit  386.     Belgian  female. 

Given  1  cc  of  1  per  cent  caffein  for  each  100  grams,  through  stomach  tube. 


Date. 


Aug.  17. 
Aug.  18. 


Weight. 


Grams. 
1,300 
1,215 


Treat- 
ment. 


13.0 
12.0 


Date. 


Aug.  19. 


Weight. 


Grams. 
(?) 


Treat- 
ment. 


(?) 


August  20:  Found  dead  9  a.  m.    Autopsy:  Lungs  slightly  congested;  liver  engorged 
and  friable;  gall  cyst  well  filled. 
Rabbit  389.     Black  male. 

Given  1  cc  of  1  per  cent  caffein  for  each  100  grams,  through  stomach  tube. 


Date. 

Weight. 

Treat- 
ment. 

Date. 

Weight. 

Treat- 
ment. 

Aug.  17 

Grams. 
1,070 

cc. 
10.0 

Aug.  18. . .  . 

Grams. 
1,025 

cc. 
10.0 

August  19:  Found  dead  9  a.  m.    Autopsy:  Lungs  severely  congested  and  partially 
hepatized;  liver  was  engorged;  other  organs  appeared  normal. 
Rabbit  382.     Belgian  female. 

On  August  17  weighed  1,035  grams;  received  1  cc  of  1  per  cent  caffein  for  each  100 
grams;  10  cc  of  1  per  cent  caffein  given  in  all. 

August  18:  Found  dead  9  a.  m.     Autopsy:  Lungs  congested  and  hepatized;  liver 
engorged;  stomach  showed  numerous  petechial  hemorrhages  on  mucosa;  kidneys 
slightly  congested;  intestines  appeared  normal. 
Rabbit  385.    Belgian  female. 

Given  1  cc  of  1  per  cent  caffein  for  each  100  grams,  through  stomach  tube. 


Date. 


Aug.  17. 
Aug.  18. 
Aug.  19. 


Weight. 


Grams. 
780 
760 
755 


Treat- 
ment. 


8.0 
7.5 
7.5 


Date. 


Aug.  20. 
Aug.  21. 


Weight. 


Grams. 
715 
700 


Treat- 
ment. 


7.0 
7.0 


August  22:  Found  dead  9  a.  m.  Autopsy:  Lungs  exhibited  pneumonic  lesions, 
with  inflammation  of  adjacent  pleura;  a  fibro-plastic  exudate  present  around  lung; 
liver  showed  a  coccidial  infestation;  stomach  distended  with  ingesta;  mucous  mem- 
brane characterized  by  a  catarrhal  inflammation;  contents  of  small  intestine  liquid 
in  nature  and  bile  stained;  large  intestine  somewhat  impacted;  liver  and  kidneys 
seemingly  normal. 


CHRONIC    lis' TOXIC ATION iiABBITS. 


71 


Rabbit  404.     While  male. 
Given  1  cc  1  per  cent  caffein  for  each  100  grama. 


Date. 


Aug.  20... 
Aug.  21... 
Aug.  22>. 
Aug.  23... 
Aug.  24.. 
Aug.  25  s 
Aug.  2()... 
Aug.  27. . 
Aug.  28'. 
Aug.  29.. 


Weight. 


Grams. 
l.-Uio 
1,475 


1,475 
1,400 
1,405 
1,415 
1,400 


Treat- 
ment. 


14.5 
14.5 


14.5 
14.0 
14.0 
14.0 
14.0 


1,310 


13.0 


Date. 


Aug.  30 
Aug.  31 
Sept.  1 . 
Sept.  2. 
Sept.  3. 
Sept.  4. 
Sept.  5. 
Sept.  6. 
Sept.  7. 
Sept.  8. 


Weight. 


Grams. 
1,320 
1,330 
1,335 
1,315 
1,350 
1,335 
1,350 
1,380 
1,375 
1.325 


Treat- 
ment. 


13.0 
13.5 
13.5 
13.0 
13.5 
13.5 
13.5 
14.0 
14.0 
13.0 


1  Not  fed. 


2  Reflexes. 


September  9:  Found  dead  9  a.  m.  Autopsy:  Both  lungs  showed  extensive  pneu- 
monia, with  adhesions  to  pleura;  pleuritis  and  pericarditis  very  marked;  large  amount 
of  fibrous  exudate  in  pleural  cavity;  pyloric  end  of  stomach  slightly  congested;  liver 
congested;  other  organs  normal. 

Rabbit  393.    Belgian. 
Given  1  cc  of  1  per  cent  caffein  to  each  100  grams,  through  stomach  tube. 


Date. 


Weight. 


Aug.  17.. 
Aug.  IS.. 
Aug.  19.. 
Aug.  20. . 
Aug.  21.. 
Aug.  22  1. 
Aug.  23.. 
Aug.  24.. 


Grams. 
950 
910 
895 
910 
905 


825 
870 


Treat- 
ment. 


9.5 
9.0 
9.0 
9.0 
9.0 


8.0 
8.5 


Date. 


Aug.  25. . 
Aug.  26.. 
Aug.  27... 
Aug.  281. 
Aug.  29. . 
Aug.  30  8. 
Aug.  311. 


Weight. 


Grams. 
835 
780 
765 


710 


Treat- 
ment. 


8.5 
8.0 
7.5 


1  Not  fed. 


2  Condition  very  poor;  not  fed. 


September  1:  Found  dead.  Autopsy:  Lungs  congested  and  adhering  to  the  pleura; 
extensive  inflammation  of  pleura;  liver  slightly  enlarged  and  congested;  mucosa  of 
stomach  and  small  intestines  slightly  congested;  other  organs  normal. 

Rabbit  390.     Belgian,  male. 
Given  1  cc  of  1  per  cent  caffein  to  each  100  grams  through  stomach  tube. 


Date. 


Weight. 


Aug.  17 
Aug.  18 
Aug.  19 
Aug.  20 


Grams. 
1,490 
1,370 
1,365 
1,340 


Treat- 
ment. 


15.0 
14.0 
13.5 
13.5 


Date. 


Aug.  21. 
Aug.  22  1 
Aug.  23. 


Weight. 


Grams. 
1,265 


1,120 


Treat- 
ment. 


12.5 


11.0 


I  Not  fed. 


August  24:  Found  dead  9  a.  m.  Autopsy:  Heart  and  lungs  appeared  normal; 
abdominal  viscera  showed  no  apparent  pathologic  change  other  than  coccidial  infec- 
tion of  the  liver  and  fullness  of  the  blood  vessels. 


72 


THE    TOXICITY   OF   CATFEIN. 


Rabbit  392.     Maltese,  female. 
Given  1  cc  of  1  per  cent  caffein  to  each  100  grams  through  stomach  tube. 


Aug.  17.. 
Aug.  18.. 
Aug.  19. . 
Aug.  20. . 
Aug.  21.. 
Aug.  22  1 
Aug.  23.. 
Aug.  24.. 
Aug.  25.. 


Date. 


■Weight. 


Orams. 
1,265 
1,275 
1,240 
1,220 
1.245 


1.180 
1.190 
1.155 


Treat- 
ment. 


12.5 
12.5 
12.5 
12.0 
12.5 


12.0 
12.0 
11.5 


Aug.  26. 
Aug.  27. 
Aug.  28  1 
.Vug.  29. 
Aug.  30. 
Aug.  31. 
Sept.  1 . . 
Sept.  2.. 


Date. 


Weight. 


Grams. 
1,140 
1,140 


1,115 

1,080 

1,020 

995 

930 


Treat- 
ment. 


11.5 
11.5 


11.0 
•11.0 
10.0 
10.0 
9.0 


1  Not  fed. 


Died  at  3  p.  m.  September  2.     Autopsy:  The  stomach  and  small  intestines  showed 
numerous  small  hemorrhagic  spots;   a  thick  coating  of  mucus  surrounded  the  con- 
tents of  the  stomach;  the  other  organs  were  apparently  normal. 
Rabbit  403.     Black. 

Given  1  cc  of  1  per  cent  caffein  for  each  100  grams.  i 


Date. 


Weight. 


Treat- 
ment. 


.Vug.  20.. 
.Vug.  21.. 
.Vug.  221. 
Aug.  23.. 
Aug.  24.. 
Aug.  25.. 


Grams. 
1,640 
1,640 


1,490 
1,515 
1.475 


16.5 
16.5 


15.0 
1.5.0 
15.0 


Date. 


Aug,  26.. 
Aug.  27.. 
Aug.  281. 
Aug.  29.. 
Aug.  30.. 


Weight. 


Grams. 
1,390 
1,330 


1,130 
1,055 


Treat- 
ment. 


14.0 
13.5 


11.5 
10.5 


1  Not  fed. 


p.  m.     Autopsy:   Extensive  gastroenteritis;  liver 
slightly    congested;  peritoneum    thickened    and 


August  31:  Found  dead  at  3 
enlarged  and  congested;  spleen 
congested;  other  organs  normal. 

Rabbit  384.     Black,  female. 
Given  1  cc  of  1  per  cent  caffein  for  each  100  grams  through  stomach  tube 


Aug.  16.. 
Aug.  17.. 
Aug.  18.. 
Aug.  19.. 
Aug.  20.. 
Aug.  21.. 
Aug.  221. 
Aug.  23.. 
.Vug.  24.. 


Date. 


Weight. 


Grams. 
1,195 
1,205 
1,140 
1.180 
1,145 
1,145 


1.005 
1,035 


Treat- 
ment. 


12.0 
12.0 
11.5 
12.0 
11.5 
11.5 


10.0 
10.5 


Aug.  25.. 
Aug.  26.. 
Aug.  27.. 
Aug.  281. 
Aug.  29.. 
Aug.  30  2. 
Aug.  31.. 
Sept.  1... 


Date. 


Weight. 


Grams. 
990 
960 
955 


870 
850 
810 
740 


Treat- 
ment. 


10.0 
9.5 
9.5 


9,0 
8,5 
8.0 
7.5 


.Vot  fed. 


i^oor  condition,  mucus  from  rectum. 


September  2:  Found  dead  at  9  a.  m.  Autopsy:  The  mucosa  of  stomach  showed 
numerous  hemorrhagic  spots;  the  first  portion  of  the  small  intestines  was  slightly 
congested;  the  other  organs  were  apparently  normal  in  appearance. 


CHRONIC   INTOXICATION RABBITS. 


73 


Rabbit  SSS.     Belgian ,  female . 
Given  1  cc  of  1  per  cent  caffein  for  each  100  grains  through  Btomach  tube. 


Date. 


Aug.  16 
Aug.  17 
Aug.  18 
Aug.  19 
Aug.  20 
Aug.  21 


Weight. 

Treat- 
ment. 

Orams. 

cc. 

995 

10.0 

1,005 

10.0 

990 

10.0 

895 

9.0 

945 

9.5 

965 

9.5 

Date. 


Aug.  22  ' . 
Aug.  2:}.. 
Aug.  24.. 
Aug.  25. . 
Aug.  26.. 
Aug.  27.. 


Weight. 


QramH. 


875 
855 
850 
785 
710 


Treat- 
ment. 


9.0 
8.5 
8.5 
8.0 
7.0 


"  Not  fed. 

August  28:  Found  dead  at  9  a.  m.  Aulnpsif:  Lung.s,  heart,  and  epleen  apparently 
normal;  liver  infected  with  coccidia;  stomach  apparently  normal;  walls  of  small 
intestines  injected;  colon  marked  congestion  and  hemorrhagic;  kidneys  hemorrhagic. 

Rabbit  S87.     Belgian  male. 
Given  1  cc  of  1  per  cent  caffein  for  each  100  grams  through  stomach  tube. 


Date. 


Aug.  17.. 
Aug.  IS.. 
Aug.  19.. 
Aug.  20. . 
Aug.  21.. 
Aug.  221. 
Aug.  23. . 
Aug.  24. . 
Aug.  25. . 


Weight. 


Grams. 
1,200 
1,340 
1,335 
1,300 
1,325 


1,205 
1,200 
1,285 


Treat- 
ment. 


12.5 
13.0 
13.0 
13.0 
13.0 


12.0 
12.0 
12.5 


Date. 


Aug.  2G. 
Aug.  27. 
Aug.  28 1 
Aug.  29. 
Aug.  30. 
Aug.  31. 
Sept.  1 . 
Sept.  2. 


Weight. 


Grams. 
1,185 
1,255 


1,115 
1,135 
1,175 
1,050 
900 


Treat- 
ment. 


12.0 
12.5 


11.0 
11.5 
12.0 
10.5 
9.0 


1  Not  fed. 

September  3,  found  dead.    Autopsy:    Stomach  and  small  intestines  showed  num- 
erous hemorrhagic  spots;  thick  coating  of  mucus  surrounded  the  contents  of  the  stom- 
ach; bladder  was  greatly  distended  with  urine;  the  other  organs  were  apparently 
normal. 
Rabbit  388.    Belgian  male. 

Given  1  cc  of  1  per  cent  caffein  for  each  100  grams,  through  stomach  tube. 


Aug.  17.. 
Aug.  18. . 
Aug.  19. . 
Aug.  20. . 
Aug.  21. . 
Aug.  22'. 


Date. 


Weight. 


Grams. 
1,080 
1,115 
1,150 
1.130 
1,120 


Treat- 
ment. 


10.0 
11.0 
11.5 
11.5 
11.0 


Date. 


Aug.  23.. 
Aug.  24. . 
Aug.  25. . 
Aug.  20. . 
Aug.  27.. 
Aug.  28 1. 


Weight. 


Grams. 
1,020 
985 
960 
900 
875 


Treat- 
ment. 


10.0 
10.0 
9.5 
9.0 
9.0 


>  Not  fed. 


August  29,  found  dead  9  a.m.  Autopsy:  Heart  and  lungs  normal ;  liver  and  kidneys 
engorged;  stomach  normal;  intestines  showed  a  catarrhal  inflammation,  though  not 
severe;  spleen  normal;  walls  of  colon  somewhat  injected. 


74 


THE    TOXICITY    OF    CAFFEIlSr. 


Rabbit  391.     Belgian. 

Given  1  cc  of  1  per  cent  caffein  to  each  100  grams  through  stomach  tube. 


Date. 


Aug.  17. 
Aug.  18. 
Aug.  19. 
Aug.  20. 
Aug.  21. 
Aug.  221 
Aug.  23. 


Weight. 


Grams. 
940 
950 
955 
935 
945 


835 


Treat- 
ment. 


9.5 
9.5 
9.5 
9.5 
9.5 


8.5 


Date. 


Aug.  24. . . 
Aug.  25. . . 
Aug.  26... 
Aug.  27  2 
Aug.  28  1 
Aug.  29. . 


Weight. 


Grams. 
805 
800 
765 
690 


565 


Treat- 
ment. 


8.0 
8.0 
7.5 
7.0 


5.5 


1  Not  fed. 


2  Poor  condition. 


August  30,  found  dead  9  a.  m.  Autopsy:  Heart  injected;  lungs  normal;  liver  affected 
slightly  with  coccidiidea;  stomach  normal  in  appearance;  small  intestines  normal, 
but  colon  considerably  inflamed;  kidneys  slightly  engorged;  other  organs  normal. 

Rabbit  402.    Black  female. 

Given  1  cc  of  1  per  cent  caffein  to  each  100  grams. 


Date. 


Aug.  20. . 
Aug.  21.. 
Aug.  22  1 
Aug.  23.. 
Aug.  24. . 
Aug.  25. . 
Aug.  26. . 


Weight. 


Grams. 
2,030 
1,950 


1,955 
1,905 
1,890 
1,780 


Treat- 
ment. 


20.0 
19.5 


19.5 
19.0 
19.0 
18.0 


Date. 


Aug.  27. 
Aug.  28  1 
Aug.  29. 
Aug.  30. 
Aug.  31. 
Sept.  1.. 


Weight. 


Grams. 

1,765 


1,630 
1,540 
1,510 
1,425 


Treat- 
ment. 


17.5 


16.5 
15.5 
15.0 
14.0 


1  Not  fed. 

September  2,  found  dead  9  a.  m.  Autopsy:  The  lungs  were  badly  congested,  the 
posterior  lobe  of  the  right  lung  showing  hepatization;  the  liver  was  considerably 
enlarged  and  congested;  the  mucous  membrane  of  the  stomach  and  small  intestines 
was  congested  and  showed  numerous  hemorrhagic  spots;  the  kidneys  showed  slight 
congestion;  all  other  organs  normal. 

Series  D.  . 

The  evidence  brought  forth  in  the  preceding  pages  regarding  cumulation  of  caffein 
naturally  suggests  the  question  whether  or  not  the  body  acquires  a  tolerance  for  it. 
This  question  has  already  been  answered  in  the  affirmative  by  Gourewitch,^^  but 
owing  to  the  method  he  used  for  the  identification  of  caffein  and  the  few  experiments 
made  his  results  are  not  conclusive.  The  experiments  of  series  A,  B,  and  C  might 
be  regarded  as  indicating  that  tolerance  for  caffein  is  not  acquired  by  the  rabbit.  It 
was  noticed,  however,  that  the  rabbit  apparently  does  tolerate  increasingly  larger 
doses  under  certain  conditions,  as  the  following  experiments  show: 

Rabbit  223.     Belgian  hare,  male. 

October  22:  Weight,  1,520  grams;  15  cc  2  per  cent  caffein  injected  subcutaneously 
at  2  p.  m. 

November  1:  10.30  a.  m.,  weight,  1,510  grams;  17  cc  2  per  cent  caffein  injected 
subcutaneously  (225  mg  per  kilo),  reflexes  observed,  but  no  tetanus. 

November  4:  10.30  a.  m.,  weight  ,1,535  grams;  19  cc  2  per  cent  caffein  injected 
subcutaneously  at  2.40  p.  m.;  4.40  p.  m.,  no  symptoms. 

November  8:  Weight,  1,425  grams;  20  cc  2  per  cent  caffein  (285  mg  per  kilo)  injected 
at  11.45  p.  m.;  5  p.  m.,  no  symptoms. 

November  17:  Weight,  1,325  grams;  22  cc  2  per  cent  caffein  injected  at  2.55  p.  m. 
(329  mg  per  kilo),  no  symptoms. 

November  18:  Rabbit  in  good  condition. 


CHRONIC   INTOXICATION — DOGS.  75 

Rabbit  224.     Belgian  hare,  female.     Diet,  carrots. 

October  18:  Weight,  1,935  grams;  11.20  a.  m.,  15  cc  2  per  cent  caffein  (155  mg  per 
kilo)  injected. 

November  I :  Weight,  1,780  grams;  20  cc  2  per  cent  caffein  (224  mg  per  kilo)  injected 
subcutaneously,  reflexes  increa-sed,  muscle  tremors  present,  but  no  otner  symptoms. 

November  4:  Weight,  1,710  grams;  21.5  cc  2  per  cent  calfein  (252  mg  per  kilo) 
injected. 

November  8:  Weight,  1,435  grams;  22.5  cc  2  per  cent  caffein  or  314  mg  per  kilo 
injected  at  11.40  p.  m.;  5  a.  m.,  no  symptoms. 

November  17^  Weight,  1,340  grams;  24  cc  2  per  cent  caffein  (358  mg  per  kilo) 
injected  subcutaneously. 

November  18:  9  a.  m.,  rabbit  died. 
Rabbit  226.     Gray  mule.     Diet,  carrots. 

October  28:  Weight,  1,045  grams;  10  cc  2  per  cent  caffein  injected  subcutaneously 
at  1.50  p.  m.;  4.30  p.  m.,  tremors  observed,  but  no  other  symptoms. 

October  29:  Rabbit  in  good  condition. 

November  1:  Weight,  950  grams;  10.55  a.  m.,  11  cc  2  per  cent  caffein  injected  sub- 
cutaneously (231  mg  per  kilo). 

November  4:  Weight,  930  grams;  2.50  p.  m.,  12  cc  2  per  cent  caffein  injected  sub- 
cutaneously (258  mg  caffein  per  kilo). 

November  6:  Weight,  945  grams;  11.45  a.  m.,  15  cc  2  per  cent  caffein  (313  mg  per 
kilo)  injected  subcutaneously. 

November  17:  Rabbit  still  alive;  weight,  890  grams. 

The  results  of  these  experiments  indicate  that  when  sufficient  time  is  allowed 
between  two  successive  injections,  susceptibility  to  caffein  is  not  increased.  The 
rabbit,  on  the  contrary,  seems  to  acquire  a  tolerance  for  the  drug,  for  the  fourth  dose 
was  15  per  cent  larger  than  the  minimum  fatal  dose  of  caft'ein.  This  is  in  all  proba- 
bility due  to  the  better  elimination  of  caffein  and  its  products  of  decomposition  and 
to  recovery  from  the  deleterious  effects  of  each  dose,  made  possible  by  long  intervals 
between  injections. 

The  results  of  these  experiments  may  be  briefly  summed  up  by  stating  that  sub- 
minimum  doses  of  caffein  given  to  the  rabbit  daily  or  at  intervals  (not  too  long)  do 
not  produce  any  symptoms  such  as  were  observed  in  acute  caffein  intoxication, 
namely,  increased  reflexes  and  convulsions,  or  increased  rate  of  respiration,  thus 
showing  that  it  is  not  cumulative.  But  evidence  of  undoubted  summation  of  effect 
wixs  adduced  to  show  that  if  the  administration  of  subminimum  doses  of  caffein 
be  continued  daily  for  a  period  of  11  to  18  days  the  result  is  fatal.  Tolerance, 
however,  may  be  acquired,  although  to  a  limited  extent  only,  provided  sufficiently 
long  intervals  between  injections  are  allowed  to  give  time  for  repair  of  the  injury 
done  by  the  drug  and  to  develop  a  mechanism  for  its  better  decomposition  and  elimi- 
nation. Furthermore,  the  evidence  just  given  indicates  that  the  elimination  of  sub- 
minimum  doses  of  caffein  and  its  products  of  decomposition  is  probably  accomplished 
within  24  hours  or  thereabouts.  That  the  elimination  of  larger  doses  is  not  accom- 
plished in  this  interval  is  made  probable  by  the  following  experiment: 

Gray  rabbit  455.     Female.     Diet,  oats. 

October  12:  Weight,  1,185  grams;  3.30  p.  m.,  11.5  cc  2  of  per  cent  caffein  injected 
into  the  lumbar  muscles;  3  p.  m.,  reflexes  increased. 

October  13:  10  a.  m.,  rabbit  weighed  1,070  grams;  no  symptoms  of  caffein  poisoning, 
reflexes  normal;  10.30  a.  m.,  10  cc  2  per  cent  caffein  injected  into  the  lumbar  muscles; 
11.30  a.  m.,  rabbit  jumped  off  the  table,  had  convulsions,  and  died. 

EXPERIMENTS  ON  DOGS. 

Having  gained  some  information  respecting  the  eft'ects  of  repeated  doses  of  caffein 
on  rabbits,  it  was  of  interest  to  find  out  how  carnivora  reacted  to  the  drug  when  simi- 
larly administered.  A  number  of  dogs  were  used  for  the  purpase.  Considerable 
variation  in  the  mode  of  experimentation,  as  will  appear  later,  was  allowed. 

Since  the  condition  of  the  animal,  its  age,  environment,  or  diet  might  be  factors 
influencing  toxicity,  tests  were  made  on  full-grown  and  on  young  growing  dogs  whose 


76  THE   TOXICITY   OF    CAFFEIN. 

food  was  varied.  The  subjects  of  the  experiment  were  kept  under  observation  for 
a  few  days  to  several  weeks  before  the  administration  of  caffein  was  begun,  in  order 
to  determine  whether  or  not  any  morbid  condition  existed,  as  well  as  to  ascertain 
whether  the  new  environment  had  any  effect  on  these  animals.  Caffein  was  given 
chiefly  by  mouth,  but  the  subcutaneous  method  was  also  employed  during  a  por- 
tion of  the  experimental  period  in  some  dogs.  The  initial  dose,  which  varied  for 
different  individuals,  was  maintained  for  a  variable  length  of  time.  It  was  then 
progressively  increased,  in  most  cases  until  the  death  of  the  animal.  With  larger 
doses  the  intervals  between  successive  injections  were  also  increased. 

Series  A. 

■  Six  dogs  were  used  in  this  series.  Caffein  was  administered  by  mouth  for  periods 
of  six  days  to  five  weeks.  It  was  given  daily  or  at  intervals  of  two,  and  sometimes  of 
three,  days.  In  a  few  instances  the  drug  was  withheld  for  four  or  even  for  seven 
days,  and  its  administration  was  resumed  at  the  end  of  this  time.  The  initial  dose 
in  these  experiments  varied  approximately  between  40  and  140  mg  per  kilo.  The 
doses  were  then  increased  gradually,  and  thus  the  maximum  resistance  of  the  subject 
to  caffein  was  tested.  The  diet  consisted  either  exclusively  of  meat  or  largely  of 
carbohydrates  with  a  minimum  amount  of  meat  to  give  flavor  to  the  food. 

Dog  11.     Female. 

Diet  consisted  of  rice,  250  grams;  cane  sugar,  250  grams;  meat,  50  grams;  cracker 
meal,  about  100  grams.  Caffein  was  given  by  mouth  daily  or  at  intervals  of  one  day, 
when  the  dose  did  not  exceed  1.5  grams.  Before  the  dose  was  increased  to  2  grams,  or 
approximately  0.213  gram  caffein  per  kilo,  an  interval  of  two  days  was  allowed.  Symp- 
toms were  noticed  the  next  day.  An  interval  of  two  days  was  therefore  allowed  again 
at  the  end  of  which  the  same  dose  was  repeated.  It  will  be  remarked  that  there  were 
no  symptoms  this  time,  and  the  general  condition  of  the  dog  seemed  to  be  good.  Two 
grams  of  caffein  were,  therefore,  given  daily  during  the  next  two  days  without  any 
untoward  effects;  the  dose  was  then  increased  to  2.5  grams.  Even  after  this  enormous 
quantity  no  symptoms  were  observed  except  slight  tremors.  When  this  dose  was 
repeated  26  hours  later,  it  proved  fatal.  No  albumin  or  sugar  was  found  in  the  urine, 
although  the  dog  was  fed  on  a  very  liberal  carbohydrate  diet.  The  following  is  a 
complete  record  of  the  experiment. 

April  20:  Urine  acid,  no  albumin,  no  sugar. 

April  21:  Urine  free  from  sugar. 

April  22:  Urine  free  from  sugar.    1  gram  caffein  given  in  the  afternoon. 

April  23:  9  a.  m.,  dog  was  very  thirsty,  drank  a  large  quantity  of  water,  urine  did 
not  reduce  Fehling's  solution. 

April  24:  2.30  p.  m.,  1  gram  caffein,  no  sugar  in  urine. 

April  25:  1  gram  caffein  administered. 

April  26:  Weight,  10.6  kilos,  urine  collected  in  the  morning,  no  sugar;  4.10  p.  m., 
1.5  grams  caffein. 

April  27:  1.5  gi-ams  caffein;  1.30  p.  m.,  diet  as  before,  no  sugar  in  urine. 

April  28:  Weight,  10.2  kilos,  no  caffein,  no  sugar  in  urine. 

April  30:  Weight,  10.4  kilos,  no  sugar  in  urine;  4.20  p.  ra.,  2  grams  caffein. 

May  1:  Urine  examined,  sugar  absent,  weight  10  kilos,  vomited,  sick,  tremors 
observed,  drank  500  cc  water  at  one  time,  appetite  poor. 

May  2:  No  caffein,  drank  150  cc  water. 

May  3:  Urine,  no  sugar,  moderate  quantity  of  albumen  present;  12  noon,  2  grams 
caffein  given  by  mouth,  weight  10.3  kilos;  2  p.  m.,  urine,  sugar  negative,  condition 
of  dog  good,  no  symptoms  of  caffein  intoxication. 

May  4:  10  a.  m.,  about  10  cc  thick,  dark-colored  mucilaginous  urine  found  in  col- 
lecting bottle;  albumin  a  little  more  than  a  trace,  decidedly  less  than  on  May  3, 
no  sugar,  condition  of  dog  pretty  good  except  for  slight  muscular  tremors;  4  p.  m., 
2  grams  caffein  by  mouth  (as  usual). 

May  5:  Urine  not  examined,  no  symptoms;  4  p.  m.,  2  grams  caffein. 

May  6:  Urine  not  examined;  2.30  p.  m.,  2.5  grams  caffein  given  by  mouth;  4  p.  m., 
slight  tremor,  no  other  symptoms. 

May  7:  No  examination  of  urine,  no  symptoms  observed;  4  p.  m.,  2.5  grams 
caffein. 

May  8:  9  a.  m.,  found  dead,  urine  collected  since  last  dose  of  caffein  was  given 
did  not  contain  any  sugar  or  albumin,  the  amount  of  caffein  fed  to  this  dog  was  18 


CHRONIC  INTOXICATION — DOGS.  77 

grams  in   18  days.     Autopsy:  Post-mortem   examination   showed   marked   enteritis 
with  hemorrhaj^c  spots  on  the  mucosa;  liver  and  kidneys  conj^ested  and  dark  colored; 
Lungs  congested;  thyroid  gland  was  greatly  enlarged  and  congested. 
Dog  23: 

April  30:  Weight,  (5.8  kilos;  the  diet  consisted  of  250  grams  rice,  250  grams  sugar, 
100  grams  cracker  meal,  and  iOO  grams  of  meat.  (Jii  May  :5  his  weight  was  7  kilos. 
He  received  1  gram  of  caffoin  by  mouth  at  12  noon.  At  2  p.  m.  he  vomited  and 
tremors  were  observed.  Tlie  next  day,  May  4,  tremors  were  still  present  though  less 
pronounced.  Examination  of  the  urine  for  sugar  and  albumin  was  nei,'ative;  on 
May  4,  1  graqi  caffein  was  given  again  and  repeated  on  May  5.  On  this  date  his  general 
condition  was  not  good — dog  had  no  appetite  and  refu.sed  to  take  caffein.  As  tiie  dog 
lost  10  per  cent  of  his  weight  he  was  put  on  a  meat  diet  exclusively  and  the  do.se  of 
caffein  was  reduced  to  0.5  gram.  He  became  sick  after  the  second  dose,  and  the 
administration  of  caffein  was  therefore  discontinued.  It  was  resumed  after  five  days 
and  the  caffein  was  administered  in  increasing  amounts,  i.  e.,  on  May  18,  0.5  gram; 
May  19,  0.5;  May  20,  1;  !May  21,  1  gram  in  two  doses  of  0.5  each,  given  at  intervals  of 
one  hour;  !May  22,  1  gram.  Dog  became  irritable,  but  no  other  symptoms  were 
observed.  The  administration  of  caffein  was  omitted  the  next  day.  On  the  follow- 
ing day  when  the  same  dose  of  caffein  was  given  there  was  again  marked  irritability 
and  tremors.     The  experiment  was  therefore  discontinued. 

Dog  22.     Male  bulldog. 

June  24:  Dog  weighed  13.7  kilos.  Diet  consisted  of  meat  exclusively;  1  gram 
caffein  was  given  by  mouth;  diarrhea  developed;  no  caffein  was  given  for  three 
days. 

June  28:  Dog  weighed  13.6  kilos,  1.5  grams  caffein  given  at  10  a.  m. 

June  30:  1.75  grams  caffein  administered. 

July  2:  Dog  weighed  13.5  kilos;  2  grams  caffein  or  0.15  gram  per  kilo,  caused  well- 
marked  thirst,  but  did  not  produce  any  other  symptoms. 
Dog  20.     Female: 

May  12:  Weight,  7.7  kilos.  Fed  liberal  carbohydrate  diet,  consisting  of  rice,  100 
grams;  sugar  100  grams;  meat  and  cracker  meal,  a  sufficient  quantity  to  flavor  the 
food. 

May  14:  Weight,  7.7  kilos.  Examination  of  urine  for  albumin  and  sugar  gave 
negative  results.     Urine  was  acid  to  litmus. 

May  17:  Weight,  7.4  kilos.  Three  hours  after  it  was  fed  the  dog  received  -0.5 
gram  caffein  by  mouth.  The  test  of  the  urine  the  next  day  for  sugar  was  negative, 
but  a  trace  of  albumin  was  present.  It  will  be  noticed  that  the  doses  were  increased 
gradually  and  that  symptoms  were  observed  only  after  the  fourth  dose  of  0.1  gram 
per  kilo.  Later  meat  was  substituted  for  the  carbohydrate  diet  and  the  administra- 
tion of  caffein  was  stopped  for  four  days.  At  the  end  of  this  period  100  mg  caffein 
per  kilo  was  fed  daily  for  five  days,  and  the  dose  was  then  very  gradually  increased. 
Diarrhea  occurred  twice,  but  no  other  symptoms,  the  second  attack  having  lasted 
a  few  days.    The  following  is  a  complete  record  of  the  experiment: 

May  19:  0.5  gram  caffein  11.45  a.  m. 

May  20:  0.75  gram  caffein  12.45  a.  m. 

Afay  21:  0.75  gram  caffein  12  noon;  no  sugar,  no  albumin  in  urine. 

May  22:  0.75  gram  caffein;  urine,  same  condition  found;  no  symptoms. 

May  23:  Weight,  7.5  kilos;  no  caffein. 

May  24:  0.75  gram  caffein;  tremors  very  marked. 

May  25:  No  caffein. 

May  26:  0.75  gram  caffein. 

May  27:  0.75  gram  caffein. 

May  28:  0.75  gram  caffein. 

May  29:  1  gram  caffein  in  two  doses  of  0.75  and  0.25  gram. 

May  30:  No  caffein. 

May  31:  No  caffein;  meat  diet  exclusively. 

June  1:  No  caffein;  meat  diet  exclusively. 

June  2:  No  caffein;  no  sugar,  no  albumin  in  urine. 

June  3:  Weight,  7.6  kilos;  0.75  gram  caffein;  no  sugar  in  urine. 

June  4:  Weight,  7.3  kilos;  0.75  gram  caffein;  no  sugar  in  urine. 

June  5:  W'cight,  7.5  kilos;  0.8  gram  caffein;  drank  500  cc  water;  ate  200  grams  meat. 

June  6:  Weight,  7.4  kilos;  0.8  gram  caffein;  500  cc  urine,  drank  500  cc  water;  ate 
200  grams  meat;  no  symptoms. 

June  7:  Weight,  7.7  kilos;  0.8  gram  caffein  10  a.  m.;  400  cc  urine,  500  cc  water,  200 
grams  meat. 


78 


THE    TOXICITY   OF    CAFFEIN. 


June  8:  Weight,  7.5  kilos;  0.9  gram  caffein,  450  cc  urine,  1  p.  m.;  200  grams  meat, 
500  cc  water. 

June  9:  Weight,  7.6  kilos;  0.9  gram  caffein,  1  p.  m.;  500  cc  water,  200  grams  meat 
and  bone  dust;  diarrhea  and  restlessness  all  afternoon. 

June  10:  Weight,  7.6  kilos;  1  gram  caffein,  500  cc  water,  200  grams  meat,  480  cc 
urine. 

June  11:  Weight,  8  kilos;  1  gram  caffein,  470  cc  urine,  500  cc  water,  200  grams  meat. 

June  12:  Weight,  7.8  kilos;  1  gram  caffein,  710  cc  urine,  500  cc  water,  200  grams 
meat. 

June  13:  450  cc  urine,  500  cc  water,  300  grams  meat. 

June  14:  Weight,  7.9  kilos;  1.2  grams  caffein,  500  cc  water,  300  grams  meat,  490 
cc  urine. 

June  15:  Weight  7.8  kilos,  500  cc  water,  300  grams  meat,  550  cc  urine. 

June  16:  Weight  8.0  kilos,  1.2  gram  caffein,  500  cc  water,  800  grams  meat,  bone  dust 
added  to  check  diarrhea. 

June  17:  500  cc  water,  300  grams  meat,  450  cc  urine,  diarrhea  continues,  bone  dust 
added. 

June  18.  Weight  7.8  kilos,  1.3  gram  caffein,  300  grama  meat,  500  cc  water,  300  cc 
urine. 

June  19:  Dog  very  thirsty,  drank  1  liter  of  water  and  ate  350  grams  of  meat;  960 
cc  urine  passed  during  the  past  24  hour. 

June  21:  Weight  7.5  kilos,  1.5  grams  caffein  given  at  10  a.  m.     At  2  p.  m.  convul- 
sions and  death.     This  dog  received  a  total  of  21.15  grams  caffein  in  25  doses  during 
a  period  of  35  days,  which  amounts  to  an  average  of  85  mg  per  kilo  daily. 
Dog  19.     Female  fox  terrier. 

May  13:  Weight  6.4  kilos.  Diet  consisted  of  rice,  100  grams;  sugar,  100  grams;  and 
a  sufficient  quantity  of  meat  and  cracker  meal  to  give  flavor  to  the  food.  Examina- 
tion of  the  urine  showed  a  trace  of  albumin  but  no  sugar.  The  urine  was  acid  to  litmus. 
Two  days  later  the  urine  was  alkaline  to  litmus.  There  was  still  a  small  amoimt  of 
albumin  but  no  sugar. 

May  17,  0.5  gram  caffein  was  given  by  mouth.  Examination  of  the  urine  collected 
the  next  day  still  showed  the  presence  of  albumin  and  the  absence  of  reducing  sub- 
stances.    The  dog  had  tremors.     Caffein  was,  therefore,  not  administered. 

May  19:  0.5  gram  caffein  was  given  by  mouth. 

May  20:  0.75  gram  caffein  was  fed  at  12.45  p.  m.  The  dog  vomited  during  the  night 
and  tremors  were  observed  the  next  morning.  The  urine  collected  was  examined 
for  albumin  and  sugar,  but  neither  was  found. 

May  21 :  12  noon,  0.75  gram  caffein  was  fed.  The  dog  weighed  6  kilos,  which  there- 
fore repro.-ented  a  loss  of  0.4  kilo.  Grew  abnormally  thirsty  and  lost  appetite,  but 
no  other  symptoms  of  caffein  poisoning  were  observed. 

May  22:  The  dog  was  again  given  0.75  gram  caffein  at  12  noon.  The  examination 
of  the  urine  for  albumin  and  sugar  gave  negative  results.  The  dog  died  at  4.15  p.  m. 
The  fatal  dose  for  this  dog  was  therefore  0.125  gram  caffein  yjer  kilo,  and  the  total 
amount  of  caffein  ingested  in  six  days  amounted  to  3.25  grams,  or  0.54  gram  per  day, 
which  makes  90  mg  per  kilo. 
Dor)21.     While  fe ma k  hull. 

This  dog  was  kept  on  a  diet  exclusively  of  meat,  and  was  given  water  ab  libitum. 
From  0.5  to  0.6  gram  of  caffein  was  administered  daily  for  seven  days;  the  doses  were 
then  increased  and  were  given  at  longer  intervals.  No  symptoms  of  the  effects  of 
caffein  were  observed  until  a  dose  of  1.5  gram  was  fed,  when  diarrhea  was  noticed  on 
the  next  day.     Jn  the  following  record  the  details  of  the  experiment  are  given: 


Dale. 

Weight. 

Caffein. 

Date. 

Weight. 

Caffein. 

Kilos. 
12.5 
12.5 
12.5 
12.3 
12.3 
12.3 
12.3 
12.3 

Grams. 
0.5 
.5 
.5 
.6 
.6 
.6 
.6 
.8 

June  16 

Kilos. 
12.7 
12.9 
13.4 
13.3 
0) 
13.5 
13.5 

Grams. 
0.8 

June  8                                ... 

June  18 

1.0 

June  21 

1.2 

June  24 

1.5 

June  25 

.0 

June  12 

June  27 

1.5 

June  13                         

June  30 

1.75 

» Diarrhea. 


CHRO>;iC    INTOXICATION DOGS.  79 

July  2:  11.30  a.  m.,  2.0  pram  caffein  fed  by  nioulh;  1.30.J).  ni.,  tetanu.",  dojr  died. 
The  totiil  amount  of  calfein  fed  to  dog  No.  21  out  of  the  25  days  of  the  experiment  was 
14. -lo  grams,  or  an  average  of  578  mg  per  day,  \vhi<h  amounts  to  about  42  to  4:i  mg  per 
kilo  of  body  weight. 

Notwithstanding  the  diversity  in  the  method  of  experimentation,  there  was  a 
striking  uniformity  in  some  of  the  results  obtained.  All  the  experiments  of  the  series 
showed  absence  of  cumulative  action  of  caffein.  The  experimental  evidence  pre- 
sented indicate.^  that  moderately  large  doses  may  be  given  at  interval.-^  of  ab<nit  24 
hours  without  inducing  any  symptoms  of  nervous  or  any  other  disturbance.  This  is 
illustrated  in  the  tests  on  dog  11,  which  were  preliminary  in  character.  In  this  sub- 
ject 100  to  150  mg  of  caffein  per  kilo  were  ingested  daily  for  several  day.s  without 
showing  any  changes.  Later  in  the  course  of  the  experiment,  after  larger  doses  were 
given,  mild  symptoms  only,  such  as  tremors,  were  observed.  Additional  evidence  of 
the  absence  of  cumulative  action  of  caffein  was  furnished  by  the  results  of  the  following 
experiments: 

Dog  23  received  142  mg  of  caffein  per  kilo  on  three  successive  days.  His  general 
condition  indicated  that  these  amounts  of  caffein  were  toxic,  but  he  survived.  In 
another  series  of  tests,  made  after  he  was  allowed  to  rest  a  few  days,  he  again  failed  to 
show  any  cumulation  of  the  drug,  as  he  survived  this  time  a  series  of  tests  of  longer 
duration  than  the  first. 

A  much  better  illustration  of  the  absence  of  cumulative  action  of  the  drug  is  fur- 
nished by  the  experiments  on  dog  No.  20.  In  this  case  100  to  125  mg  of  caffein  per 
kilo,  given  on  10  consecutive  days,  did  not  cause  any  marked  effects.  Diarrhea  and 
restlessness  were  the  only  symptoms  observed.  These  experiments  therefore  show 
that  the  elimination  and  decomposition  of  caffein  are  apparently  effected  by  the  body 
within  twenty-four  hours  or  thereabouts. 

Experiments  on  dog  19,  however,  form  an  exception — the  third  dose  of  125  mg  caf- 
fein per  kilo  ha\'ing  proved  fatal.  The  very  low  protein  content  of  the  diet  of  this 
dog  suggests  itself  as  a  possible  cause  of  the  lower  resistance  to  caffein  of  this  subject. 
But  it  may  be  observed  that  the  same  diet  was  furnished  to  dog  20,  which  stood  such 
amounts  of  caffein  much  longer.  The  presence  of  a  trace  of  albumin  in  the  urine  of 
dog  19  is  likewise  inadmissible  as  a  cause  of  the  difference  in  the  toxicity  of  caffein 
in  this  dog,  for  the  urine  of  dog  20  likewise  contained  a  trace  of  albumin.  The  alkaline 
reaction  of  the  urine,  together  with  the  fact  that  the  first  dose  of  only  60  mg  of  caffein 
per  kilo  induced  symptoms  of  toxicity,  su^ests  the  presence  of  an  abnormal  condition 
which  in  all  probability  was  the  cause  of  the  death  of  this  subject  under  the  conditions 
indicated. 

In  a  lai^e  number  of  experiments  on  caffein  performed  in  this  laboratory  it  has  been 
observed  that  symptoms  due  to  caffein  often  disappeared  when  the  administration  of 
the  same  dose  of  the  drug  was  continued.  Thus  dog  19  vomited  when  the  amount  of 
caffein  was  increased  to  125  mg  per  kilo.  WTien  this  amount  was  repeated  the  next 
day  there  was  no  vomiting.  Similar  observations  were  made  on  dogs  11  and  23,  also 
on  other  dogs.  No.  22  developed  diarrhea  at  first;  when  the  adminLstration  of  caffein 
was  resumed  several  days  later,  however,  there  was  no  diarrhea.  In  other  experi- 
ments performed  in  this  laboratory,  symptoms  of  nervous  irritability  induced  by 
caffein  disappeared  on  continued  treatment. 

It  was  interesting,  therefore,  to  inquire  whether  resistance  to  caffein  would  be 
increased  by  the  continued  administration  of  progressively  larger  amounts  of  the  drug. 
When  doses  of  150  and  over  were  fed,  the  intervals  allowed  were  usually  longer  than 
24  hours.  Two  and  sometimes  three  days  were  permitted  to  elapse  between  two  suc- 
cessive doses.  This  was  done  in  order  to  allow  time  for  recovery  from  possible  changes 
induced  by  larger  doses  of  caffein,  and  thus  prevent  the  summation  of  effect.  In  the 
experiment?  considered,  therefore,  Nos.  11,  23,  20,  and  19,  the  toxicity  of  caffein  does 
not  seem  to  be  greater  than  in  the  experiments  on  acute  caffein  intoxication  in  the 


80  THE   TOXICITY   OF    CAFFEIN. 

dog.     It  was  thought,  however,  that  the  large  initial  doses  or  the  quick  change  to  large 

doses  when  the  amounts  used  in  the  beginning  were  small,  might  have  something  to 

do  with  failure  to  induce  a  marked  degree  of  tolerance.    The  experiment  on  dog  21 

was  therefore  carried  out  by  giving  from  40  to  60  mg  per  kilo  for  eight  days,  and  then 

increasing  the  dose,  but  tolerance  could  not  be  induced,  as  is  shown  in  the  protocol 

to  the  experiment. 

Series  B. 

According  to  the  studies  of  Chittenden,''^  low  protein  diet  improves  the  general 
metabolism  of  the  body,  fatigue  is  diminished,  and  bodily  vigor,  therefore,  corre- 
spondingly increased.  The  expectation  is,  therefore,  justified  that  the  defense  of  the 
organism  against  deleterious  substances  introduced  into  the  body  is  much  improved 
by  such  a  diet,  thus  increasing  its  resistance  to  poisons.  Hunt's  experiment  on  this 
subject,  also  quoted  by  Chittenden,  lends  support  to  this  view.  He  found  that  mice 
fed  on  carbohydrates  chiefly,  or  on  foods  containing  only  a  small  amount  of  protein, 
were  more  resistant  to  acetonitril.  It  was  interesting,  therefore,  to  inquire  whether 
the  toxicity  of  caffein  differs  under  similar  conditions  of  diet. 

A  fixed  diet  of  the  same  calorific  value  was  provided  for  all  dogs  of  this  series,  but 
the  protein  content  for  three  of  the  animals  was  approximately  one-third  of  the  amount 
visually  fed  to  dogs.  Caffein  was  at  first  administered  subcutaneously,  but  all  the  dogs 
on  a  low  protein  diet  developed  abscesses  at  the  site  of  injection,  while  none  of  those 
on  high  protein  diet  showed  a  local  reaction.  Feeding  by  mouth  was  then  begun 
and  continued  throughout  the  experiment  in  each  case.  The  initial  dose  was  50  mg 
per  kilo,  which  was  given  daily  for  seven  to  nine  days.  It  was  then  increased  pro- 
gressively by  25  mg  per  kilo;  75  mg  per  kilo  were  administered  for  one  to  two  days, 
100  mg  for  two  to  three  days,  125  mg  for  one  to  two  days,  150  mg  for  one  to  two  days, 
and  a  single  dose  of  175  mg.  It  will  be  remarked  that  sometimes  an  interval  of  one 
day  had  to  be  allowed  during  which  no  caffein  was  fed. 
Dog  30.     Black  and  tan  hound,  male. 

The  dog  was  under  observation  for  about  eight  weeks  before  the  experiment  was 
begun  and  had  received  a  high  protein  diet.  He  was  then  given  50  mg  caffein  for  nine 
consecutive  days.  On  the  tenth  day  the  dose  was  increased  to  75  mg  per  kilo.  As  no 
symptoms  developed,  this  dose  was  increased  to  100  mg  per  kilo,  and  was  fed  one  day 
apart.  It  was  then  raised  to  125  mg  per  kilo.  For  the  first  time  since  the  drug  was 
fed,  symptoms  appeared;  they  were  noticed  a  few  hours  after  feeding  and  persisted 
during  the  next  day.  Although  the  appetite  was  good,  no  caffein  was  given  on  this 
day.  On  the  following  day  this  dose  was  repeated.  As  the  symptoms  were  not  serious, 
150  mg  per  kilo  were  given  daily  for  the  next  three  days,  until  175  mg  per  kilo  was 
reached.     This  dose  proved  fatal  within  six  hours.     Record  of  experiment  follows: 

October  9:  Weight,  9  kilos,  on  full  nitrogen  diet,  received  daily  0.724  gram  nitrogen 
per  kilo  or  87  calories  per  kilo,  received  18  grams  meat  per  kilo,  4  grams  lard  per  kilo, 
3  grams  carbohydrates  per  kilo,  bone  dust,  ad  libitum. 

November  3:  Weight,  9.10  kilos. 

November  10:  Weight,  9  kilos. 

November  20:  Weight,  9.55  kilos. 

November  29:  Weight,  8.70  kilos. 

December  6,  7,  8,  and  9:  Received  subcutaneously  22  cc  2  per  cent  caffein.  Condi- 
tion good,  site  of  injection  normal. 

Deceml:)er  10,  11,  12,  13,  and  14:  Received  0.4375  gram  caffein  by  mouth  equal  to 
0.050  gram  per  kilo,  no  symptoms,  appetite  and  general  condition  good. 

December  15:  11.30  a.  m.,  received  0.6563  gram  caffein  by  mouth,  or  0.75  gram  per 
kilo,  no  symptoms,  appetite  good,  condition  excellent. 

December  16:  11  a.  m.,  received  0.870  gram  caffein  l)y  mouth,  or  0.1  gram  per  kilo, 
weight  8.70  kilos,  no  symptoms. 

December  17:  No  caffein  given. 

December  18:  Received  0.870  gram  caffein,  or  0.1  gi-am  per  kilo,  no  symptoms. 

December  20:  2.45  p.  m.,  received  1.0875  grams  caffein,  or  0.125  per  kilo;  4  p.  m.,- 
ate  food  readily,  seemed  very  uncomfortable  and  sick. 

December  21:  9  a.  m.,  stiffness  in  muscles,  but  no  other  symptoms,  appetite  good, 
no  caffein  given. 


CHRONIC   INTOXICATION DUGS.  81 

December  22:  11  a.  m.,  received  1.0875  grams  caffein,  or  0.125  gram  per  kilo;  3  p.  m., 
depressed  in  spirits  and  sick,  but  no  other  symptoms  observed. 

Decemi)er  23:  11.30  a.  m.,  received  1.305  grams  caffein,  or  0.b50  gram  caffein  per 
kilo;  1.30  p.  m.,  apparently  quite  sick,  l)ut  no  other  symptoms,  had  good  appetite. 

December  24:  10  a.  m.,  received  0.175  gram  caffein  per  kilo;  4  p.  m.,  wnen  about 
to  be  fed  fell  over  and  died;  no  autopsy. 

The  total  amount  of  caffein  given  dog  30  was  11.3458  grams,  administered  for  a  period 
of  eighteen  days.  The  average  daily  amount  per  kilo  was  therefore  72  mg.  The  feces 
became  offensive  when  the  amounts  of  caffein  were  increased  to  75  mg  per  kilo.  It 
will  be  observed  that  in  this  dog  the  appetite  was  uniformly  good  until  trie  day  of  his 
death.  Whether  or  not  this  is  the  cause  of  his  resistance  to  caffein  will  be  discussed 
later. 
Dog  S2.     White,  male,  young. 

Although  he  was  growing  rapidly  this  dog's  weight  was  constant,  but  he  looked 
anemic.  He  received  a  high  protein  diet  until  Deceml)er  3,  when  the  rations  were 
increased  by  one-third.  This  dog  was  under  observation  from  October  2lj  to  December 
6  when  the  administration  of  caffein  was  begun.     He  then  received  50  mg  caffein 

§er  kilo  daily  for  nine  days  consecutively  without  showing  any  effects,  when  the 
ose  was  increased  to  75  mg  per  kilo,  then  to  100  mg  per  kilo.  This  dose  was  further 
increased  to  150  mg  per  kilo  without  causing  symptoms,  which  was  repeated  the 
next  day.  No  symptoms  having  been  observed  after  such  amounts  of  caffein,  175  mg 
per  kilo  were  fed.  This  dose,  however,  proved  fatal  within  two  hours.  Record  of 
experiment  follows: 

October  26:  Weight,  6.90  kilos. 

November  3:  Weight,  6.90  kilos. 

November  10:  Weight,  6.90  kilos. 

November  20:  Weight,  6.90  kilos. 

November  29:  Weight,  6.55  kilos. 

December  3:  Put  into  cage,  diet  increased  one-third. 

December  6,  7,  8,  9:  Weight  6.30  kilos;  12.30  p.  m.,  received  16  cc  2  per  cent  caffein 
by  subcutaneous  injection  in  back,  no  symptoms  of  any  kind  noticed,  site  of  injection 
normal. 

December  10,  14:  0.05  gram  caffein  per  kilo. 

December  15:  Received  0.4725  gram  caffein  by  mouth,  no  symptoms. 

December  16:  Received  0.655  gram  caffein,  0.100  gram  per  kilo. 

December  17:  No  caffein  given. 

December  18:  Received  0.655  gram  caffein  daily,  0.100  gram  per  kilo,  no  symptoms. 

December  20:  Received  0.8188  gram  caffein,  0.125  gram  per  kilo,  no  symptoms, 
appetite  good. 

December  21:  Received  0.9825  gram  caffein,  0.150  gram  per  kilo,  somewhat  uncom- 
fortable, no  other  symptoms. 

December  22:  Received  0.9825  gram  caffein,  0.150  gram  per  kilo,  no  symptoms 
except  some  uneasiness. 

December  23:  9a.  m.,  no  symptoms,  appetite  good ;  11.30a.  m.,  received  1.146  grams 
caffein,  0.1759  gram  per  kilo;  1.30  p.  m.,  died  while  making  an  effort  to  get  out  of  cage, 
tonic  contraction  of  limbs  observed  before  death. 

The  amount  of  caffein  received  during  the  entire  experimental  period  was  9.2223 
grams,  or  an  average  per  day  approximately  of  80  mg  per  kilo,  and  therefore  10  per  cent 
more  than  dog  No.  30  received.  It  will  be  observed  that  the  appetite  in  dog  No.  32 
was  likewise  uniformly  good,  and  that  he  received  a  very  high  protein  diet  which  was 
also  of  a  very  high  calorific  value. 

Autopsy  (dog  32). — Stomach  presented  a  severe  inflammation  of  the  mucosa,  espe- 
cially in  the  fundus  and  pyloric  portions.  The  gastritis  was  more  marked  in  pyloric 
portion,  and  the  inflammatory  condition  extended  along  the  whole  course  or  email 
intestines,  which  presented  numerous  hemorrhagic  areas,  and  a  thick  catarrhal  exudate 
on  the  mucosa.  The  large  intestine  contained  quite  a  large  number  of  parasites, 
probably  round  worms.  The  liver  was  enlarged  and  the  gall  cyst  well  filled.  The 
spleen  was  also  considerably  engorged,  kidneys  appeared  normal,  other  organs  all 
appeared  normal. 
Dog  31.    Black  spaniel,  male. 

This  dog  had  been  under  observation  one  month  previous  to  the  experiments  with 
caffein.  The  usual  initial  dose  was  then  administered  for  nine  days.  There  were  no 
signs  of  local  irritation  when  the  drug  was  given  subcutaneously,  but  symptoms  of 
toxicity  were  present.  These  disappeared,  however,  when  the  drug  was  administered 
by  mouth.  The  dose  was  therefore  increased  to  75  mg  per  kilo.  This,  as  will  be  seen, 
proved  fatal  within  six  hours.     High  nitrogen  diet,  same  as  No.  30. 

November  3:  Weight  10.250  kilos. 

18594°— Bull.  148—12 6 


82  THE   TOXICITY    OF    CAFFEIX. 

November  10:  Weight,  10.25  kilos. 

November  20:  Weight,  10.30  kilos. 

December  1:  Put  in  cage. 

December  6,  7,  8,  9:  Weight,  10.20  kilos;  received  26  cc  2  per  cent  caffein  Bubcu- 
taneously,  site  of  injection  normal. 

December  6:  Very  restless  and  excited,  whined  when  handled  as  though  muscles 
were  sore,  appeared  to  be  sick. 

December  10-14:  Condition  good,  received  0.51  gram  caffein  by  mouth  daily,  no 
noteworthy  symptoms,  apjietite  continues  good,  somewhat  restless  at  intervals. 

December  15:  11.30  a.  m.,  received  0.765  gram  caffein  per  mouth  (0.075  gram  per  '. 
kilo);  2  p.  m.,  depressed  in  spirit,  seemed  sick  and  uncomfortable;  4.15  p.  m.,  when  ' 
about  to  feed,  animal  jumped  up,  then  fell  back  dead. 

Autopsy  (dog  31):  Lungs  congested;  heart  tilled  with  blood  and  contained  small 
amount  of  blood-stained  fluid  m  pericardial  sac.  Liver  deeply  congested,  soft  and 
friable;  gall  bladder  distended  with  bile;  kidneys  showed  inflammation  of  cortex; 
spleen  pale,  normal  in  size  and  consistency;  stomach  practically  empty,  the  mucosa  of 
the  pyloric  portion  exhibited  severe  gastritis,  with  thick  catarrhal  exudate.  This 
catarrhal  inflammation  extended  through  the  duodenum;  remaining  portion  of  small 
intestine  showed  mild  inflammation;  large  intestine  appeared  practically  normal. 
The  total  amount  of  caffein  received  by  dog  31  during  10  days  was  5.395  mg,  or  a  daily 
average  of  53.9  mg  per  kilo.  This  unusually  low  resistance  to  caffein  ^which  was 
practically  the  only  case  in  all  the  experiments  on  dogs  presented  in  this  research) 
suggests  the  presence  of  some  abnormal  condition.  The  bloody  exudate  in  the  peri- 
cardial cavity  indicating  pericarditis,  which  is  likely  to  induce  secondary  changes  of 
cardiac  muscle,  may  be  considered  as  a  possible  cause  of  the  increased  toxicity  of 
caffein  in  this  case. 
Dog  29.     Male  fox  terrier,  black. 

This  dog  was  kept  on  a  low  nitrogen  diet  for  nearly  five  weeks  before  the  feeding  of 
caffein  was  begun.  The  administration  of  50  mg  of  caffein  per  kilo  was  then  carried 
on  for  eight  days  without  showing  any  symptoms  of  toxicity.  The  usual  increase  of 
dose  was  then  given — 75  mg  per  kilo — which  was  followed  by  a  manifestation  of 
symptoms.  Further  increase,  however,  to  100  mg  per  kilo  had  no  visible  effect. 
Nevertheless  it  was  considered  advisable  to  suspend  the  feeding  of  caffein  for  one  day. 
The  same  amounts  were  then  repeated  on  two  consecutive  days.  No  symptoms  having 
been  observed,  125  mg  per  kilo  were  given.  As  symptoms  of  toxicity  and  especially 
loss  of  appetite  were  observed,  the  dog  was  not  given  any  caffein  the  next  day.  Since 
his  appetite  had  now  improved,  the  experiment  with  larger  doses  was  resumed.  Death 
followed  after  the  second  dose  of  150  mg  per  kilo.    Protocol  follows: 

Weight,  9.90  kilos.  One-third  nitrogen  diet.  Receives  0.269  gram  nitrogen  per 
kilo  (88.269  calories  per  kilo). 

November  3:  Weight,  9.85  kilos. 

November  10:  Weight,  9.55  kilos. 

November  12:  Weight,  9.40  kilos. 

November  29:  Weight,  9.85  kilos. 

December  6:  Weight,  9.90  kilos;  11.35  a.  m.,  received  25  cc  2  per  cent  caffein  solu- 
tion by  subcutaneous  injection  in  back;  4  p.  m.,  no  sj'mptoms,  appetite  good. 

December  7-9:  Received  25  cc  caffein  2  per  cent  solution — subcutaneous  injection, 
no  symptoms,  area  of  injection  inflamed  and  swollen. 

December  10,  13:  Site  of  injection  showed  increased  inflammation,  received  0.495 
gram  caffein  (50  mg  per  kilo)  in  30  grams  meat  daily  without  showing  any  symptoms. 

December  14:  12  noon,  received  0.7425  gram  caffein  by  mouth  (0.075  per  kilo);  2.30 
p.  m.,  restless  and  uneasy. 

December  15:  11.30  a.  m.,  received  0.7425  gram  caffein  by  mouth;  2  p.  m.,  depressed^ 
in  spirits,  although  continues  to  have  good  appetite. 

December  16:  Weight,  9.50  kilos;  3.15  p.  m.,  received  0.9509  gram  caffein  by 
mouth;  4.50  p.  m.,  no  symptoms. 

December  17:  Animal  rested. 

December  18:  Received  0.950  gram  caffein  by  mouth,  no  symptoms. 

December  19:  Received  0.9509  gram  caffein  by  mouth,  no  symptoms. 

December  20:  2.45p.m.,  received  1.1875  grams  caffein  (0.125  gram  per  kilo);  4  p.m., 
restless  and  quite  sick;  ate  only  a  little  food. 

December  21:  9  a.  m.,  etill  uncomfortable,  allowed  to  rest,  no  caffein  given,  grad- 
ually recovered  appetite. 

December  22:  11  a.  m.,  received  1.875  grams  caffein;  3  p.  m.,  seemed  sick,  but 
showed  no  other  symptoms,  appetite  fair. 

December  23:  9  a.  m.,  showed  no  symptoms  from  the  day  before,  ate  food  grad- 
ually, seemed  sick;  11.30  a.  m.,  received  1.425  grams  caffein  (0.150  gram  per  kilo);  1.30 


CHRONIC   INTOXICATION — DOGS.  83 

p.m.,  looked  and  behaved  as  if  very  sick,  no  other  Kymptoms;  3.45  p.  m.,  in  attempting 
to  get  out  of  box  fell  over  on  back,  had  convuIsionH,  whined,  dyspnoea,  died  within  30 
seconds. 

Autopsy:  Stomach  exhibited  mild  inflammation;  small  intestine  inflamed  and  hem- 
orrhagic area.s  on  mucosa;  liver  engorged  and  friable;  spleen  normal;  kidneys  slightly 
congested;  other  organs  appeared  normal.  The  total  amount  of  caffein  fed  to  Dog  29 
was  12.135  grams,  which  was  given  in  18  days.  The  average  daily  amount  per  kilo 
was  therefore  07. 08  mg. 
Dog  28.     Male  fox  terrier. 

Low  nitrogen  diet  was  begun  about  four  weeks  before  the  feeding  of  caffein;  50  mg 
of  caffein  was  then  fed  for  seven  consecutive  days.  Partial  loss  of  appetite  was 
observofl  after  the  first  dose.  As  the  experiment  progressed  the  desire  for  food  steadily 
diminished,  and  the  feces  became  fetid.  Symptoms  of  intoxication  manifested  them- 
selves early  in  the  experiment,  and  vomiting  occurred  after  the  fourth  dose.  The 
dog  was  then  put  on  a  diet  exclusively  of  meat.  After  an  intermission  of  10  days  109 
mg  caffein  per  kilo  were  given.  Since  there  were  no  symptoms,  the  following  day  the 
amount  was  increased  to  125  mg  per  kilo.     This  dose  proved  fatal  within  IG  to  20  hours. 

This  dog  was  stout  and  strong,  weight  12.25  kilos,  received  daily  0.269  gram  nitrogen 
per  kilo  (88.269  calories  per  kilo). 

November  3:  Weight,  11.75  kilos. 

November  10:  Weight,  11.95  kilos. 

November  20:  Weight,  11.20  kilos.  All  through  this  period  had  been  kept  in  a  cold, 
poorly  ventilated  room,  put  in  a  warm  room,  with  bedding  and  good  Aentdation. 

November  29:  Weight,  11.95  kilos. 

December  1:  Put  in  a  cage;  weight,  11.95  kilos. 

December  6:  Weight,  11.95  kilos;  11.45  a.  m.,  received  0.050  gram  caffein  per  kilo; 
then  received  30  cc  2  per  cent  caffein  (0.6  gram)  in  practically  one  subcutaneous  injec- 
tion; 4.30  p.  m.,  ate  only  part  of  food. 

December  7:  10.25  a.  m.,  received  30  cc  2  per  cent  caffein  by  subcutaneous  injec- 
tion (0.6  gram,  or  50  mg,  per  kilo);  1.45  p.  m.,  seemed  sen.sitive  to  touch,  no  desire  for 
food,  depressed  in  spirit. 

December  8:  11.40  a.  m.,  received  30  cc  2  per  cent  caffein  by  subcutaneous  injec- 
tion (50  mg  per  kilo);  1  p.  m.,  depressed  in  spirit,  hind  legs  seemed  somewhat  stiff, 
no  desire  for  regular  food,  site  of  injection  inflamed. 

December  9:  10.50  a.  m.,  received  30  cc  2  per  cent  caffein  by  subcutaneous  injec- 
tion (50  mg  per  kilo);  2.30  p.  m.,  had  vomited,  no  desire  for  regular  food. 

December  10:  Inflammation  of  site  of  injection,  and  swelling  very  pronounced; 
2  p.  m.,  received  0.5975  gram  caffein,  or  50  mg  per  kilo,  with  30  grams  of  meat,  refused 
regular  food. 

December  11,  12:  Received  0.5975  gram  caffein  by  mouth,  no  symptoms  except 
refusal  of  regular  food,  feces  fetid. 

December  13-22:  Put  on  meat  diet  exclusively,  high  temperature,  no  caffein, 
weight  10  kilos,  appetite  good,  feces  fetid. 

December  22:  12  m.,  weight  11  kilos,  received  1.2  grams  caffein  by  mouth  (0.109 
gram  per  kilo);  4  p.  m.,  no  symptoms. 

December  23:  11.30  a.  m.,  received  1.375  grams  caffein  (0.125  gram  per  kilo)  had 
vomited  food  of  the  day  before,  but  could  notice  no  caffein  or  capsules  in  vomit;  4.30 
p.  m.,  no  symptoms,  seemed  in  good  .spirits,  appetite  good,  had  no  meat  to  feed  with,  so 
was  given  low  nitrogen  feed,  of  which  be  ate  about  one-fourth. 

December  24:  9a.  m.,  found  dead,  stiff,  and  cold.  The  mo.st  striking  effect  of  caffein 
in  this  dog  is  the  increased  intestinal  putrefaction.  The  feces  were  still  fetid  10  days 
after  the  administration  of  caffein  was  st(i])pod. 

Autopsy,  dog  28:  Stomach  partially  filled  witli  an  undigested  food  mass;  mucosa 
showed  severe  inflammation;  small  intestines  presented  a  hemorrhagic  enteritis  along 
whole  extent;  large  intestine  also  exhibited  mild  inflammation;  liver  was  engorged; 
spleen  appeared  normal;  kidneys  slightly  congested  in  cortical  portion;  other  organs 
appeared  normal. 

Dog  24.  White  and  tan  male:  Was  put  on  low  protein  diet  six  weeks  before  experi- 
ments with  caffein  were  begun.  The  initial  dose  of  50  mg  per  kilo  was  then  admin- 
istered on  eight  consecutive  days.  The  only  symptoms  observed  during  this  period 
of  caffein  administration  were  those  of  intestinal  putrefaction.  Fetid  feces  were 
noticed  already  after  the  first  dose  of  caffein  was  injected.  WTien  the  second  dose 
of  75  mg  of  caffein  was  repeated,  mild  symptoms  appeared,  but  none  have  been 
observed  even  with  increased  amounts  of  caffein. 

One-third  nitrogen  diet.  Received  daily  0.269  gram  nitrogen  per  kilo  (88.269 
calories  per  kilo). 


84  THE   TOXICITY   OF    CAFFEIN. 

October  26:  Weight  11.15  kilos.  Food  consisted  of  5  grams  cracker  meal  per  kilo; 
meat,  3  grams  per  kilo;  lard,  2  grams  per  kilo;  tapioca,  10.69  grams  per  kilo.  Kept  in 
a  cold,  damp  room  with  poor  ventilation  until  November  20. 

Novembers:  Weight,  11  kilos. 

November  10:  Weight,  10.75  kilos. 

November  20:  Weight,  10.55  kilos;  changed  to  a  warm  room,  with  bedding  and  good 
ventilation. 

November  29:  Weight,  10.85  kilos. 

December  1:  Put  into  a  cage. 

December  6:  Weight,  10.90  kilos;  11.25  a.  m.,  received  28  cc  2  per  cent  caffein  sub- 
cutaneously  in  side,  below  the  shoulders,  area  washed  with  alcohol  and  ether, 
approximately  50  mg  per  kilo  administered,  no  symptoms. 

December  7:  10.15  a.  m.,  received  28  cc  2  per  cent  caffein  injected  subcutaneously; 
feces  soft  and  very  fetid;  1  p.  m.,  depressed  in  spirit,  eyes  dull. 

December  9:  10.45  a.  m.,  received  25  cc  2  per  cent  caffein  solution  subcutaneously, 
feces  still  fetid,  site  of  injection  inflamed  and  swollen,  no  other  symptoms. 

December  10:  Inflammation  of  area  of  injection  more  pronounced;  2  p.  m.,  given 
0.5449  gram  caffein  and  30  grams  of  meat;  4  p.  m.,  fed,  no  symptoms,  feces  fetid. 

December  11:  12  m.,  given  0.5459  gram  caffein  and  30  grams  of  meat,  no  symptoms, 
feces  fetid. 

December  12,  13:  Given  0.5459  gram  caffein  daily,  without  noticing  any  symptoms. 

December  14:  12  m.,  received  0.817  gram  caffein  (75  mg  per  kilo);  2.30  p.  m.,  restless? 
and  uncomfortable,  no  other  symptoms. 

December  15:  11.30  a.  m.,  received  0.8175  gram  caffein  by  mouth;  2  p.  m.,  depressed 
in  spirit,  acted  as  though  sick,  no  other  symptoms. 

December  16:  Weight,  11  kilos;  11  a.  m.,  received  0.100  gram  caffein  per  kilo  (1.100 
grams)  by  mouth,  no  symptoms. 

December  17:  Rested. 

December  18:  2.30  p.  m.,  received  1.100  grama  caffein  by  mouth;  4.  p.  m.,  no 
symptoms. 

December  19:  12  noon,  received  1.100  grama  caffein  by  mouth;  4.15  p.  m.,  no 
symptoms. 

December  20:  2.45  p.  m.,  given  1.375  grama  caffein  (0.125  gram  per  kilo);  3.45  p.  m., 
vomited — one  of  the  capsules  being  found  intact,  the  other  broken  open;  4  p.  m., 
given  regular  diet,  containing  1.3757  grams  caffein  in  capsules,  ate  most  of  this  during 
the  night,  whined  at  intervals,  coordination  disturbed,  appeared  very  sick,  but 
exhibited  no  other  symptoms. 

December  21:  9  a.  m.,  found  dead,  stiff,  and  cold. 

The  total  amount  of  caffein  received  by  dog  24  was  between  10.109  and  11.484  grama. 
As  one  of  the  capsules  vomited  was  intact  and  the  other  broken  open,  the  amount  was 
probably  about  10.75  grams.  The  fatal  dose  in  this  case  was  tmdoubtedly  less  than 
185  mg  per  kilo — somewhere  between  125  and  185  mg.  Autopsy  showed  heart  in 
diastole;  posterior  lobe  of  right  lung  deeply  congested;  liver  engorged;  gall  cyst  filled; 
spleen  appeared  normal;  stomach  well  filled  with  semifluid  mass;  pyloric  portion  of 
stomach  exhibited  a  severe  inflammation  of  mucosa;  mucosa  of  duodenum  greatly 
inflamed  and  showed  hemorrhagic  areas  and  catarrhal  exudate;  remainder  of  small 
intestine  also  exhibited  mild  inflammation;  kidneys  deeply  engorged,  mesentery 
injected. 

A  comparison  of  the  fatal  doses  of  caffein  in  the  experiments  on  high  and  low  protein 
diet  does  not  show  much  difference  in  the  resistance  to  caffein,  since  175  mg  per  kilo 
proved  fatal  to  Nos.  30  and  32,  while  No.  29  died  after  receiving  150  mg  per  kilo,  and 
No.  24  received  125  to  185  mg  per  kilo.  Moreover,  No.  28,  which  was  changed  from 
low  to  high  protein  diet,  succumbed  when  given  125  mg  per  kilo.  Observations  made 
during  the  experimental  period  indicate,  however,  greater  toxicity  of  caffein  in  the 
subjects  on  low  protein  diet.  Dog  30  showed  the  effects  of  the  drug  when  the 
dose  was  increased  to  125  mg  of  caffein  per  kilo,  while  in  No.  32,  150  mg  per  kilo  were 
received  without  any  manifestation  of  symptoms.  Dog  31,  which  was  likewise  on  a 
high  protein  diet,  is  evidently  an  exception,  and  its  low  resistance  to  caffein  may  be 
accounted  for  by  the  condition  found  at  autopsy.  In  other  dogs  on  low  protein  diet 
symptoms  of  intoxication  appeared  early  in  the  experiment.  In  Noa.  29  and  24  it 
was  observed  as  soon  as  the  amount  of  caffein  was  increased  to  75  mg  per  kilo.  In 
dog  28  the  first  dose  of  caffein  50  mg  per  kilo  was  toxic.  The  symptoms  of  gastro- 
intestinal disturbance  were  especially  marked  after  caffein  on  low  protein  diet.    This 


CHRONIC   INTOXICATION DOUS.  85 

may  seom  to  contradict  the  results  of  oxperinicnt.H  on  dotjH  11  and  20,  in  which  larger 
dosen  of  caffein  failed  to  induce  symptoms  of  intoxication.  But  it  should  be  observed 
that  the  diet,  which  consisted  almost  exclusively  of  carbohydrates,  was  given  only 
during  the  administration  of  caffein,  while  in  the  experiments  of  series  B  the  sub- 
jects received  a  low  protein  diet  for  several  weeks  before  the  administration  of  caffein 
was  begun,  and  it  was  continued  through  the  entire  caffein  period.  It  will  be  re- 
marked that  the  absence  of  cumulative  action  in  the  experiments  of  the  preceding 
series  was  also  observed  in  dogs  on  high  as  well  as  on  low  protein  diet.  The  appearance 
of  symptoms  after  smaller  doses  of  caffein  in  the  latter  experiments  might  suggest 
cumulative  action,  but  since  these  symptoms  disappeared  on  continued  administration 
of  the  substance  cumulation  is  clearly  not  indicated.  The  gastrointestinal  lesions 
obeerved  on  post-mortem  examination  were,  it  will  be  recalled,  also  found  in  rabbits 
similarly  treated.  The  explanation  suggested  probably  applies  also  in  the  case  of 
dogs. 

Series  C. 

As  already  pointed  out  in  the  experiments  on  acute  toxicity  of  caffein,  young  growing 
dogs  are  probably  more  resistant  to  caffein  than  adults.     That  this  may  also  hold  true 
in  chronic  caffein  intoxication  seemed  indicated  by  the  following  experiments. 
Dog  SS.    Black  female  puppy.     Weight,  4  kilos.     Had  been  continuously  on  a   vuat 

diet. 

December  22:  2.30  p.  m.,  received  0.69  gram  of  caffein  (0.172  gram  per  kilo);  3.15 
p.  m.,  no  symptoms  except  that  feces  were  fetid. 

December  23:  11.30  a.  m.,  received  0.79  gram  of  caffein  (0.197  gram  per  kilo);  1.30 
p.  m.,  no  symptoms. 

December  24:  11  a.  m.,  received  0.87  gram  of  caffein  (0.2009  gram  per  kilo);  4  p.  m., 
no  symptoms. 

It  will  be  observed  that  the  only  effect  produced  in  dog  33  by  feeding  caffein  was 
increased  intestinal  putrefaction,  although  2.37  grams  of  caffein  were  given  in  three 
days.  Additional  data  on  the  effects  of  the  age  of  animals  on  the  resistance  to  caffein 
seemed  desirable.  The  following  experiments  were  therefore  carried  out.  Six  puppies 
of  the  same  litter  were  weaned  when  7  to  8  weeks  old  and  put  on  a  milk  diet.  Three 
of  them  received  this  diet  throughout  the  experimental  period.  Meat  was  substituted 
in  the  other  three  a  few  days  before  the  administration  of  caffein  was  begun,  and  waa 
continued  until  the  end  of  the  experiment.  Caffein  was  given  by  mouth;  the  initial 
dose,  which  was  administered  for  several  days  and  then  gradually  increased,  being 
IGO  to  200  mg  for  each  dog,  except  one,  which  received  only  100  mg  per  kilo  for  several 
days  and  then  an  increased  amount. 


86 


THE   TOXICITY   OF    CAFFEIN. 


An  intermission  of  a  few  days  (during  which  no  caffein  was  given)  was  allowed. 
This  was  done  on  account  of  some  studies  carried  on  at  the  same  time  on  the  effect  of 
caffein  on  certain  constituents  of  the  urine. 


PUP  NO.  1. 


Date. 

Weight. 

Food 
(milk). 

Treatment 

(2  per  cent 

caffein). 

Symptoms. 

Apr.21 

Grains. 
1,450 
1,520 
1,450 
1,375 
1,420 
1,390 
1,400 
1,405 
1,420 
1,430 
1,450 
1,515 
1,475 
1,495 
1,515 
1,535 
1,525 
1,530 
1,500 

1,490 
1,535 
1,460 
1,475 
1,545 
1,550 
1,555 
1,500 
1,450 
1,500 
1,565 
1,545 

1,595 

1,495 

cc. 
300 
300 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 

250 
250 
300 
350 
250 
250 
250 
250 
250 
250 
250 
250 
250 
250 

250 

cc. 
10.0 
10.0 
10.0 
10.0 
10.0 

None. 

None. 

None. 

None. 

None. 
10.0 
15.0 
15.0 
15.0 
22.0 
20.0 
20.0 
20.0 
23.0 

None. 

25.0 
None. 
None. 
None. 
None. 
None. 

25.0 
None. 
None. 
None. 
None. 
None. 

27.0 

27.0 

No  sjrmptoms. 

Apr.  22 

Do. 

Apr.  23 

Do. 

Apr.24 

Do. 

Apr.  25  . . 

Do. 

Apr.  26  . . .          

Apr.  27 

Apr.  28 

Apr.29 

Passed  worms. 

Apr.  30 

Do. 

May  1                

No  symptoms. 

May  2 

Do. 

May  3 

Do. 

May  4 

Do. 

May  5 

Seems  dull  and  whines. 

May  6. .             

Whines. 

May  7 

No  symptoms. 

May  8 

Do. 

May  9 

Diarrhea;    passed  worms;  tremor  and  rigidity  of 

May  10 

legs;  whines. 
Completely  recovered  from  the  effects  of  9th. 

May  11 

Can  not  balance  itself;  continually  vomiting. 

May  12 

Recovered  from  eflects. 

May  13 

In  good  condition. 

May  14 

May  15 

May  16 

May  17 

Salivated  in  cage;  stiffness  of  muscles. 

May  18. 

Weak  and  stiff;  diarrhea. 

May  19. 

No  symptoms. 

May  20 

May  21 

May  22 

May  23 

Tremors;  gait  clumsy;  incoordination    of  move- 

May 24 

ments. 
Diarrhea;  vomited;  weak    and   stiff;  found    dead 

9  a.  m.  25th. 

>  Sunday. 

Autopsy:  Marked  pulmonary  congestion;   liver  very  pale;  heart  wall    injected; 
slight  inflammation  of  stomach  and  intestines. 


Date. 


CHRONIC   INTOXICATION — PUPPIES. 
PUP  NO.  2. 


87 


■Weight. 


Oramx. 
1.S50 
1.240 
1.250 
1.205 
1,220 
1,210 
1,210 
1,205 
1,200 
1.210 
1,220 
1 .  220 
1.2.35 
1,235 
1,2.35 
1,250 
1,235 
1,250 
1,1(15 
1,2;« 
1,300 

1,200 
1.215 
1,280 
1,300 
1,310 
1,310 
1,250 
1,245 
1,310 
1,325 
1,325 
1.325 
1.315 


Fo()<l 
(milk). 


300 
300 
200 
2(J0 
200 
200 
21K) 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 

200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 
200 


Troatmont 

(2  per  cent 

callein). 


cc. 
5.0 
5.0 
7.5 
7.0 
7.0 

None. 

None. 

None. 

Nono. 

None. 
10.0 
10.0 
10.0 
10.0 
17.0 
17.0 
15.0 
15.0 
18.0 

None. 
20.0 

None. 

None. 

None. 

None. 

None. 
20.0 

None. 

None. 

None. 

None. 

None. 
22.0 
22.0 


8>-mptoms. 


!  To  symptoms. 
Do. 
Do. 
Do. 
Do. 


Pa-ssod  worms. 


No  symptoms. 

bo. 

Do. 

Do. 
Whines. 

Do. 
Diarrhea  and  worms. 
Diarrhea. 

Little  or  no  symptoms. 
No  svTnptoms. 
Salivated  in  case;  refused  to  eat;  draws  up  hind 

legs. 
Recovered. 
In  good  condition. 


Salivated  in  cage;  stiff;  all  symptoms. 
Weak  and  stifl. 
No  symptoms. 


Somewhat  stifl. 

Restless;  scratches  eyes;  sick. 


PUP  NO.  3. 


1,215 

300 

1,220 

300 

1,220 

200 

1,200 

200 

1,205 

200 

1,195 

200 

1,200 

200 

1,215 

200 

1,220 

200 

1,200 

200 

1,225 

200 

1,230 

200 

1.235 

200 

1,245 

200 

1,270 

200 

l,2(i0 

200 

1.240 

2IX) 

1,205 

200 

1,240 

200 

None. 

None. 

None. 

None. 

None. 

None. 

(') 

None. 

None. 

None. 
10.0 
10.0 
10.0 
10.0 
17.0 

17.0 

15.0 
1.5.0 
18.0 


?'o  symptoms. 

Do. 
Coughs  and  whines. 
Passed  worms. 
Eyes  appear  dim  and  is  continually  scratching 

"them. 
Appears  restless  and  draws  up  hind  legs  when 

walking. 
Eyes  dim;  passed  worms;  diarrhea. 
Cou>,'hing  continually;  very  rest  less. 
12  noon;  salivatetl  in  cage;  passed  worms;  diarrhea; 

foaming  at  mouth;  can   not  balance   himself; 

rigidity  and  tremor  of  hind  legs.     2.15,  found 

dead. 


'  Urine  squeezed  from  bladder. 

Autopsy:  Severe  pulmonary  congestion;  catarrhal  gastritis;  mild   enteritis  with 
small  hemorrhagic  areas  on  mucosa. 


88 


THE    TOXICITY   OF   CAFFEIN". 

PUP  NO.  4. 


Date. 


Apr.  28 . 
Apr.  29 . 
Apr.  30 . 
May  1 . . 

May  2 . . 
May  3 . . 
May  4 . . 
May  5 . . 


May  6.. 
May  7. . 
Mays.. 
May  9.. 
May  10. 
May  11. 
May  12. 
May  13. 
May  14. 
May  15. 
May  16. 
May  17. 
May  18. 
May  19. 
May  20. 
May  21 . 
May  22. 
May  23. 
May  24. 
May  25. 
May  26. 
May  27. 


Weight. 


Grams. 
1,670 
1,670 
1,070 
1,690 
1,690 


1,720 
1,735 


1,760 
1,745 
1,710 
1,750 
1,750 
1,755 
1,730 
1,785 
1,835 
1,820 
1,835 
1,860 
1,855 
1,770 
1,755 
1,780 


1,785 
1,795 
1,630 
1,600 


Food. 


Milh  (.cc). 
300 
300 
300 
300 
300 
300 
300 
300 

Meat 
(grams). 
60 
80 
180 
180 
180 
180 
180 
180 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 


Treatment 

(2  per  cent 

cafleiii). 


10.0 
None. 
None. 
10.0 
10.0 
10.0 
10.0 
15.0 
15.0 
15.0 
17.0 
17.0 
17.0 


20.0 
23.0 


Symptoms. 


No  symptoms. 


Do. 

Do. 
Passed  worms. 
Feces  soft  and  black. 
Stiff;  loss  of  appetite. 
Loss  of  appetite. 

Do. 
Restless. 

Feces  soft  and  black. 
Loss  of  appetite. 

Loss  of  appetite;  threw  up  worms. 
Loss  of  appetite;  worms;  cough;  diarrhea. 
Weak;  no  appetite;  diarrhea;  cough. 
Found  dead,  9  a.  m. 


Autopsy. — Lung  uniformly  congested;  liver  deeply  congested;  heart  muscle  pale 
with  hemorrhagic  areas;  kidneys  pale  with  hemorrhagic  spots  on  surface  and  in 
cortex;  slight  catarrhal  inflammation  of  stomach  and  the  small  intestines. 


CHRONIC   INTOXICATION — PUPPIES. 
PUP  NO.  5. 


89 


Date. 


Weight. 


Food. 


Treatment 
(2  percent 
caffein). 


Symptoms. 


Apr.  28 . 
Apr.  29. 
Apr.  30. 
May  1 . . 
May  2.. 
May  3 . . 
May  4.. 
Mays.. 


May  6. . 
May  7.. 
Mays.. 
May  9.. 
May  10. 
May  11. 
May  12 . 
May  13. 
May  14. 
May  15 . 
May  If). 
May  17. 
May  18. 
May  19. 
May  20. 
May  21 . 
May  22. 
May  23. 
May  24. 
May  25. 
May  26. 
May  27. 
May  28. 
May  29. 
May  30. 
May  31 . 
June  1 . . 
June  2.. 
June  3.. 


GravM. 
1,745 
1,745 
1,750 
1,7()5 
1,765 


1,490 
1,805 


1,815 
1,825 
1,770 
1,795 
1,805 
1,800 
1,720 
1,815 
1,845 
1,830 
1,815 
1,830 
1,835 
1,825 
1,850 
1,835 


1,820 
1,835 
1,840 
1,820 
1,840 
1,830 


1,770 
1,765 
1,750 
1,635 


Milk  (cc). 
300 
300 
300 
300 
300 
300 
300 
300 

Meat 
(grams). 
60 
80 
180 
180 
180 
180 
180 
180 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 


10.0 

None. 

None. 
10.0 
10.0 
10.0 
15.0 
15.0 
15.0 
15.0 
17.0 
17.0 
17.0 
20.0 
20.0 
23.0 
25.0 
25.0 

None. 

None. 

None. 
25.0 
27.5 
27.5 


No  symptoms. 


Do. 

Do. 
Loss  of  weight;  no  other  symptoms. 
No  symptoms. 
Stiflness. 
No  symptoms. 
A  little  stiff. 
No  symptoms. 

Do. 
Do. 
Feces  soft  and  black. 

A  little  stiff. 


Diarrhea;  stiff  in  hind  legs. 

Diarrhea  and  worms. 

Paralyzed;  vomited;  died  at  3  p.  m. 


90 


THE   TOXICITY   OF    CAFFEIN. 

PUP  NO.  6. 


Date. 


Apr.  28 . 
Apr.  29. 
Apr.  30. 
Mavl.. 
May  2.. 
May  3.. 
May  4.. 
Mays.. 


May  6. . 
Mav7.. 
Mays.. 
May  9.. 
May  10. 
May  11. 
May  12. 
May  13. 
May  14. 
May  15 . 
May  16- 
Mayl7. 
May  18. 
May  19. 
May  20. 
May  21 . 
May  22. 
May  23. 
May  24. 
May  25. 
May  20. 
May  27. 
May  28. 
May  29. 


Weight.  !     Food. 


Grams. 


1,280 
1,290 
1,315 
1,330 


1,360 
1,365 


1,395 
1,365 
1,340 
1,380 
1,400 
1,425 
1,470 
1,485 
1,510 
1,500 
1,485 
1,480 
1,485 
1,495 
1,500 
1,500 


1,470 
1,465 
1,450 
1,450 
1,355 
1,270 


Milk{cc) 
300 
300 
300 
300 
300 
300 
300 
300 

Meat 
(grams). 
60 
80 
180 
180 
180 
180 
180 
180 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 
115 


Treatment 

(2  per  cent 

caffein). 


14.5 
None. 
None. 
14.5 
14.5 
14.5 
14.5 
19.5 
19.5 
19.5 
17.0 
17.0 
17.0 
20.0 
20.0 
23.0 
2.3.0 
23.0 


Symptoms. 


No  symptoms. 


Do. 
Do. 
Passed  worms. 


Feces  soft  and  black;  almost  diarrhea. 
Scratches  her  eyes  and  chases  her  tail. 


Feces  soft  and  black. 

Diarrhea  and  worms. 

Refused  to  eat  all  food. 

Threw  up  worms,  stiff,  and  has  skin  over  both  eyes. 

Found  dead. 


Highest  amount  of  caffein  given,  362  mg  per  kilo.     No  autopsy. 

Examination  of  the  results  obtained  in  the  experiments  of  series  C  shows  that 
young  and  growing  dogs  tolerate  large  amounts  of  caffein.  In  four  subjects  of  this 
series,  Nos.  1,  2,  3,  and  6,  no  effect  was  observed  when  moderately  large  amounts 
(160  to  200  mg  per  kilo  of  caffein)  were  fed.  Symptoms  were  noticed  only  when 
these  amounts  of  caffein  were  increased  from  50  to  60  per  cent.  The  other  two  dogs, 
Nos.  4  and  5,  of  this  series  were  less  resistant,  however,  to  caffein,  as  0.16  gram  of  the 
drug  per  kilo  induced  well-marked  symptoms.  Since  these  were  fed  meat,  while  Nos. 
1,  2,  and  3  received  milk,  the  difference  in  toxicity  may  be  due  to  the  diet  employed, 
but  No.  6,  which  likewise  received  a  meat  diet,  failed  to  show  the  effects  of  caffein 
when  200  mg  per  kilo  were  fed.  On  the  other  hand,  it  should  be  noticed  that  No.  1 
died  after  receiving  360  mg  per  kilo,  No.  2  survived  a  dose  of  334  mg,  while  No.  3  died 
after  a  dose  of  322  mg  per  kilo  of  caffein.  The  fatal  doses  for  Nos.  4.  5,  and  6  were  287, 
335,  and  300  mg  per  kilo,  respectively.  Although  the  differences  are  too  small  to 
justify  any  definite  conclusion  regarding  the  effect  of  a  milk  diet  or  of  a  meat  diet  on 
the  toxicity  of  caffein,  the  results  nevertheless  suggest  a  reasonable  possibility  that 
caffein  is  more  toxic  to  young  dogs  when  on  an  exclusively  meat  diet  than  when  fed 
milk.  It  is  perfectly  evident,  however,  that  the  resistance  to  caffein  in  either  case  is 
very  great,  almost  twice  that  of  adult  subjects.  As  shown  in  series  A  and  B,  125  to 
175  mg  per  kilo  proved  fatal  to  all  but  two  animals  in  these  experiments,  while 
symptoms  of  toxicity  appeared  after  much  smaller  doses.  In  other  respects  the 
behavior  of  young  dogs  toward  caffein  was  the  same  as  that  of  the  adult.  In  neither 
case  was  cumulation  nor  tolerance  observed  under  the  conditions  of  these  experi- 
ments. The  findings  at  autopsy  were  likewise  similar,  as  gastro-enteritis  was  the 
chief  lesion  observed  on  macroscopic  examination.     It  might  be  mentioned,  however, 


DI:3CUSS10>;    (Jl-    UKSL'LTS,  <Jl 

in  this  cnnnoctinn,  that  the  symptoms  of  caff  inn  intoxication  in  yoiin.!^  dojiTS  often 
presented  marked  differences  fnjin  those  observed  in  those  of  more  advanced  at^e. 
The  resemblance  of  the  effects  of  caffein  in  youns?  pnj)pies  and  in  rabbits  was  very 
atrikinij.  In  both,  the  tonic  with  clonic  convulsions  were  observed  after  a  sufficient 
quantity  of  caffein  was  administered.  In  the  dogs  which  were  fully  prown  a  large 
dose  of  caffein  was  usually  followed  by  tonic  convulsions  and  almost  instantaneous 
death. 

Moderately  large  amounts  of  caffein  fed  daily  to  pupj)ies  f(jr  several  days — in  some 
cases  as  long  as  10  days — induced  mild  symptoms  only.  No  cumulative  effect  was 
observed  in  any  of  the  experiments  of  series  C.  There  seems  to  be  tcjlerance  of  certain 
functions  toward  caffein,  but  no  general  tolerance  of  the  body  could  be  obtained  in 
these  experiments.  Caffein  is  apparently  less  toxic  for  adult  dogs  on  high  than  on  low 
protein  diet.  lu  young  and  growing  dogs  caffein  is  somewhat  less  toxic  when  milk, 
rather  than  meat,  forms  the  exclusive  diet.  Some  pathological  conditions  apparently 
increase  the  toxicity  of  caffein  also  in  dogs.  The  symptoms  of  caffein  intoxication 
observed  in  young  dogs  are  in  some  respects  different  from  those  in  full  grown  and  older 
animals,  and  resemble  those  noticed  in  rabbits. 

DISCUSSION  OF  RESULTS. 

It  was  pointed  out  at  some  length  in  the  introduction  that  the 
toxicity  of  some  drugs  may  not  be  the  same  for  all  forms  of  life. 
This  observation  was  also  made  by  some  investigators  who  experi- 
mented with  caffein  on  different  species  of  animals.  Thus  Maurel  ^^ 
stated  that  caffein  is  twice  as  toxic  for  the  frog  as  for  the  rabbit  when 
administered  by  mouth.  Froliner's  -^  experiments,  on  the  other  hand, 
made  on  domestic  animals,  failed  to  show  great  differences  in  the 
toxicity  of  caffein.  According  to  this  observer,  horses  seem  to  be 
more  susceptible  than  cattle,  goats,  and  swine,  the  minimum  toxic 
dose  being  the  same  for  all  of  these,  while  the  resistance  of  the  dog  to 
caffein  is  about  midway  between  that  of  the  horse  and  the  other 
animals  mentioned.  It  may  be  remarked,  however,  that  Frolmer  made 
only  13  experiments.  That  these  data  are  inadequate  for  the  forma- 
tion of  any  conclusions  as  to  the  toxicity  of  caffein  is  evident  since 
the  most  strikmg  effect  of  cafTein  observed  in  the  work  herein 
reported  was  the  comparatively  wide  range  of  variation  in  the  re- 
sistance of  individuals  of  the  same  species  to  this  drug.  This  was 
found  to  be  the  case  even  when  the  conditions  of  experimentation 
were  approximately  uniform,  and  was  observed  whatever  the  mode 
of  admmistration  of  the  drug  employed.  The  toxicity  for  different 
individuals  also  varied  in  acute  as  well  as  in  chronic  intoxication. 
It  is  for  this  reason  that  the  number  of  tests  employed  were  often 
quite  large,  for  no  conclusions  of  any  value  could  be  drawn  ^vithout 
averaging  the  results  of  a  sufficiently  large  number  of  experiments. 
Furthermore,  it  is  to  be  borne  in  mind  that  the  action  of  a  drug  may 
differ  according  to  the  mode  of  its  introduction  into  the  body  and 
that  different  species  of  animals  may  vary  in  this  regard.  This  is 
especially  true  of  some  substances  when  given  by  mouth,  the  range 


92  THE    TOXICITY   OF    CAFFEIlSr. 

in  toxicity  for  certain  species  of  animals  being  much  greater  when 
thus  administered  than  when  injected  subcutaneously  or  intrave- 
nously. 

Maurel's  ^^  investigations  are  of  interest  in  this  connection,  as  his 
work  embraces  a  systematic  study  of  the  toxicit}^  of  a  large  number 
of  substances  in  the  rabbit,  pigeon,  and  frog  when  given  by  mouthy 
subcutaneously,  intravenously,  or  when  injected  into  the  muscles. 
According  to  this  investigator  the  range  of  variation  of  the  toxicity 
of  a  substance  is  "wadest  when  given  by  mouth.  Potassium  sulpho- 
cyanid,  for  example,  is  about  2.5  times  as  toxic  for  the  frog  as  for  the 
rabbit  when  given  by  mouth.  Quinin  hydrobromid  is  three  times  as. 
toxic  for  the  frog  as  for  the  pigeon,  while  for  the  rabbit  it  is  twice  as 
toxic  as  for  the  pigeon.  When  given  by  hypodermic  injection  the 
toxic  dose  per  kilo  weight  is  practicall}^  the  same  for  all  three  species. 
The  difference  of  resistance  according  to  the  mode  of  administration 
is  even  more  marked  for  spartein  sulphate.  When  given  by  mouth 
the  toxicity  for  the  rabbit  is  six  times  as  great  as  for  the  frog,  but 
when  injected  subcutaneously  the  toxic  dose  is  about  the  same  for 
the  rabbit  and  for  the  frog.  The  relation  of  the  mode  of  adminis- 
tration to  toxicity  is  further  shown  in  the  following  substances :  For 
the  rabbit  the  minimum  fatal  dose  per  kilo  of  quinin  hydrobromid  is 
1.5  grams  administered  by  mouth,  0.5  gram  when  injected  subcu- 
taneously, and  0.07  gram  by  the  intravenous  path,  while  strychnui 
sulphate  is  twice  as  toxic  administered  intravenously  as  subcuta- 
neously, and  six  times  as  toxic  as  when  administered  by  mouth. 
The  mode  of  introduction,  however,  does  not  always  affect  the 
toxicity  of  a  substance.  This  is  made  evident  by  the  action  of 
strj^chnin  on  frogs  in  which,  according  to  Maurel  ^^,  the  toxic  dose  is 
the  same  whether  given  by  mouth  or  injected  into  the  subcutaneous 
tissues.  This  appears  to  hold  true  also  for  other  animals  as  demon- 
strated by  the  experiments  of  Hatcher  ^^  on  the  cat,  in  which  he 
observed  that  strychnin  is  as  readily  absorbed  from  a  full  stomach 
as  from  the  subcutaneous  tissues.  These  findings  are  extremely 
interesting,  especially  in  view  of  Maurel's  "  work  on  the  subject, 
according  to  which  he  finds  that  a  substance  is  much  less  toxic  when 
given  by  mouth  than  when  administered  by  hypodermic  injection 
or  intravenousl3\  That  tnis  generahzation  does  not  admit,  however, 
of  universal  apphcation  is  made  evident  by  the  work  of  various 
experimenters.  Claude  Bernard  ^°  observed  that  curara  is  as  poisonous 
for  the  pigeon  when  given  b}''  mouth  as  when  injected  subcutaneously, 
while  Zalesky  ^  foimd  that  samandarin  is  more  toxic  for  frogs  when 
introduced  into  the  stomach  than  by  injection  into  the  Ij^mph  sacs. 
Our  experiments  with  caffein  likewise  show  that  Maurel's  generaliza- 
tion does  not  always  hold  good,  since  it  was  found  in  experiments  mth 
gray  rabbits  that  the  minimum  fatal  dose  is  but  moderately  greater 
by  mouth  than  by  the  subcutaneous  path. 


DISCUSSION    OF    RESULTS.  93 

Equally  interestincjj  is  the  observation  of  the  writer,  that  in  the 
guinea  ])i,i;  the  difToreuce  in  the  toxicity  between  the  subcutaneous 
and  intraperitoneal  injections  is  very  sli^jht,  wliile  in  the  cat  tiie 
toxicity  of  caffein  is  the  same  whether  given  by  mouth  or  injected 
into  the  subcutaneous  tissues,  and  is  markedly  less  when  injected  into 
the  j)eritoneal  cavity.  The  experiments  on  dogs  show  considerable 
variation  of  elTective  dose  when  given  by  mouth,  but  the  interest- 
ing obsers'ation  w^is  made  that  the  toxic  dose  by  mouth  may  be 
smaller  in  some  cases  than  the  average  dose  by  subcutaneous  injec- 
tion. If  the  resistance  to  caffein  by  subcutaneous  injection  of  the 
diflferent  species  of  animals  experimented  upon  in  the  present  research 
be  compared,  it  will  be  noticed  that  the  gray  rabbit  or  Belgian  hare, 
which  is  more  resistant  than  the  other  varieties  employed,  stands 
more  caffein  in  proportion  to  the  weight  of  the  body  than  the  other 
animals. 

Although  the  minimum  fatal  dose  was  found  to  be  somewhat  larger 
for  the  guinea  pig  than  for  the  gray  rabbit  when  caffein  was  injected 
intraperitoneally,  it  was  on  the  contrary  smaller  by  other  patlis  of 
introduction,  and  approximated  quite  closely  the  minimum  fatal 
dose  for  rabbits  of  the  other  varieties.  Cats  as  well  as  dogs  were 
found  to  be  distinctly  less  resistant  to  caffein  than  the  herbivora. 

There  are  a  number  of  factors  far  more  important  than  zoological 
differences  which  influence  the  toxicity  of  caffein.  Some  of  these 
are  age,  season,  and  pathologic  conditions.  As  these  factors  have 
already  been  dwelt  upon  in  their  appropriate  places,  further  discus- 
sion might  seem  unnecessary,  but  o\ving  to  their  importance  in  deter- 
mining the  action  of  a  drug,  emphasis  is  desirable.  Especially  is  this 
the  case  with  pathological  conditions  in  relation  to  toxicity.  Wli'Je 
no  positive  proof  of  diminished  resistance  to  caffein  in  pathological 
conditions  was  obtained  by  subjecting  the  suggestion  to  experimental 
test,  it  was  observed  in  these  experiments  on  rabbits  that  death 
occurred  in  some  individuals  after  small  doses  wliich  are  usually  not 
even  toxic.  The  findings  at  autopsy  indicate  the  presence  of  patho- 
logical conditions.  The  same  was  observed  in  some  experiments  on 
cats  and  dogs.  It  is  extremely  probable,  therefore,  that  disease 
modifies  the  reaction  of  the  organism  to  caffein  as  well  as  to  other 
drugs.^^ 

That  the  resistance  to  drugs  may  var}'  according  to  the  age  of  the 
subject  has  been  maintained  by  a  number  of  pharmacologists.  Accord- 
ing to  Guinard, '"  j'oung  dogs,  rabbits,  and  guinea  pigs  are  very  sus- 
ceptible to  morpliin,  resembhng  children  in  this  regard."  The  mini- 
mum fatal  dose  for  these  animals  is  about  one-third  less  than  for  the 

a  A  case  of  accidental  poisoning  reported  recently  by  Wlchura  (Munich,  Med.  VVoch.,  1911,  No.  30,  p. 
1618)  throws  some  doubt  on  the  accepted  view  that  the  sa^ceptibllity  of  young  children  to  morphin  is 
greater  than  that  of  adults.  Wlchura  also  found  that  the  therapeutic  doses  of  codein  preparations  ordi- 
narily recommended  lor  children  in  pleuritic  cough  are  not  eSective  In  this  condition. 


94  THE   TOXICITY    OF    CAFFEII^. 

adult.  This  is  not  true,  however,  for  the  3'oung  of  other  species. 
Cats  under  15  days  of  age  tolerate  twice  the  toxic  dose  of  morphin 
for  the  adult  cat.  Young  beeves  and  goats  are  likewise  more  resistant 
to  this  alkaloid  than  adults.  On  the  other  hand,  according  to  Livon,^* 
young  guinea  pigs  are  more  sensitive  to  alkaloids  than  adults.  The 
toxicity  of  caffein,  as  shown  in  the  present  investigation,  was  found 
to  be  less  in  the  3'oung  than  in  the  adult.  In  dogs  the  3^oung  subjects 
are  in  some  instances  almost  twice  as  resistant  as  adults.  The  differ- 
ence was  found  to  be  less  in  cats  and  rabbits  than  in  dogs,  but  it  was 
quite  marked. 

The  effect  of  season  on  the  toxicit}^  of  drugs  has  been  discussed  in 
the  section  on  the  experiments  on  guinea  pigs,  which  were  more  re- 
sistant to  caffein  in  the  fall  than  in  February  and  March,  The  effect 
of  season  seems  to  vary  with  the  animal,  but  it  may  also  differ  with  the 
substance  employed.  In  Noe's  ^^  studies  on  this  subject  cantharidin 
was  found  to  be  more  toxic  for  the  hedgehog  in  November  than  in 
July.  The  effect  of  season  was  different  for  morphin,  as  it  was 
observed  that  the  resistance  of  the  hedgehog  was  greater  at  the  end 
of  the  summer  than  earlier  in  the  season. 

The  relation  of  diet  to  toxicity  of  drugs  has  been  studied  by  Hunt.^® 
His  experiments  indicate  that  this  is  an  important  factor  in  the  resist- 
ance to  acetonitril.  The  studies  here  reported  on  the  eft'ect  of  diet 
on  toxicity  of  caffein  in  rabbits  were  confined  to  experiments  with 
oats  and  carrots  and  do  not  show  any  mocUfication  of  the  resistance 
to  caffein.  The  question  of  diet  in  chronic  intoxication  in  dogs,  how- 
ever, suggests  that  in  these  animals  diet  may  affect  the  toxicity  of 
caffein,  although  the  data  on  this  subject  are  far  from  satisfactory. 
There  is  nevertheless  sufficient  evidence  to  suggest  that  a  high  protein 
diet  for  the  adult  dog  tends  to  greater  resistance  of  the  animal  to 
caffein  and  similarly  the  growing  dog  tolerates  larger  quantities  of 
caffein  on  a  milk  diet  than  on  a  diet  of  meat. 

This  brings  us  to  a  consideration  of  the  behavior  of  caffein  in 
chronic  intoxication.  Although  in  both  rabbits  and  dogs  absence  of 
cumulation  was  evident,  in  other  respects  decided  differences  in  the 
resistance  to  caffein  were  observed.  While  the  rabbit  tolerates  more 
than  tmce  the  single  dose  of  caffein  per  kilo  for  the  dog,  the  result  is 
quite  different  in  repeated  dosage  of  the  drug,  the  rabbit  succumbing 
to  continued  administration  of  much  smaller  doses  of  the  drug  than 
the  dog.  This  is  probably  due  to  lesions  of  the  gastro-intestinal  canal 
caused  by  caffein  which  occasions  loss  of  appetite  much  more  readily 
in  the  rabbit  than  in  the  dog.  The  abundant  energy  reserve  in  the 
dog  makes  it  possible  for  this  animal  to  stand  inanition  much  longer 
than  the  rabbit  and  other  herbivora.  The  difference  in  the  behavior 
of  the  rabbit  and  dog  toward  caffein  is  interesting  as  sho^ving  complete 
reversal  of  resistance  in  acute  and  chronic  intoxication.     From  the 


CONCLUSIONS.  05 

statement  in  the  introduction  it  is  evident  that  the  size  of  the  sin^jle 
toxic  or  lethal  dose  of  a  substance  is  in  no  wise  an  index  of  the  active 
dcfijree  of  its  toxicity.  The  experiments  with  caffein  here  reported 
furnish  additional  evidence  that  this  is  trne,  at  least  for  the  rabbit. 

GENERAL  SUMMARY  AND  CONCLUSIONS. 

The  toxicit}"  of  cafTeiu  in  the  rabbit  varies  with  the  mode  of  its 
administration,  he'm<i:  least  when  .iriven  by  raoutli  and  greatest  by 
intravenous  administration.  The  toxicity  is  from  15  to  20  per  cent 
greater  by  subcutaneous  injections  than  by  mou<h,  but  is  about  half 
of  that  when  injected  into  the  ])eritoneal  cavity.  \o  dilference  was 
observed  in  the  toxicity  of  calTein  whether  administered  into  gluteal 
or  into  the  lumbar  muscles.  "When  introduced  by  this  route  the 
toxicity  was  found  to  be  less  by  one-third  llian  when  it  is  injected 
into  the  peritoneal  cavity,  but  is  about  30  per  cent  more  toxic  than 
the  subcutaneous  injections.  White  or  black  rabl)its  were  found  to 
be  less  resistant  to  cafTein  than  gray  rabbits. 

The  resistance  of  the  guinea  pig  to  cafTein,  as  of  the  ra))l)it,  is 
greatest  when  given  by  mouth.  The  minimum  fatal  dose  is  less  by 
intraperitoneal  injections,  but  greater  than  by  subcutaneous  injec- 
tions, thus  differing  from  the  rabbit  in  this  regard.  The  adult  cat 
is  less  resistant  than  the  guinea  pig  or  rabbit  to  cafTein.  The  mini- 
mum lethal  dose  by  mouth  is  the  same  as  by  subcutaneous,  and  is 
less  than  by  intraperitoneal,  injection.  The  minimum  fatal  dose 
for  dogs  was  found  to  be  the  same  by  mouth  as  by  subcutaneous  in- 
jection and  is  almost  the  same  as  for  the  cat.  The  toxicity  of  cafTein 
varies  in  the  guinea  pig  according  to  season  of  the  year. 

Age  is  likewise  a  factor  in  the  toxicity  of  cafl'ein,  young  animals 
being  more  resistant  than  the  full-grown  and  older  animals;  this  was 
shown  in  experiments  on  rabbits,  cats,  and  dogs.  The  symptoms  of 
cafTein  poisoning  also  were  different  in  ])uppies  and  in  full-grown  dogs. 
Different  diets,  such  as  carrots  and  oats,  did  not  influence  the  resist- 
ance of  rabbits  and  guinea  pigs  to  cafTein.  Low  protein  diet  tends 
to  decrease  resistance  to  cafTein  in  dogs.  Young  growing  dogs  are 
less  resistant  to  cafTein  on  a  meat  than  on  a  milk  diet.  CafTein  is 
not  cumulative  in  the  rabbit  or  dog,  even  if  administered  for  a  con- 
siderable length  of  time.  Some  degree  of  tolerance  may  be  induced 
m  the  rabbit  under  certain  conditions,  but  not  in  dogs  under  the 
conditions  of  the  experiments  made  in  this  investigation.  The  possi- 
bility, however,  that  dogs  may  accjuire  tolerance  for  cafTein  is  not 
excluded.  Although  the  rabbit  tolerates  a  much  larger  single  dose 
of  cafTein  than  the  dog,  it  was  found,  in  experiments  on  clironic 
intoxication  that  the  rabbit  is  less  resistant  to  cafTein  than  the  dog. 
The  toxicity  of  cafl'ein  is  probably  increased  under  pathological  con- 


^6 


THE    TOXICITY   OF    CAFFEIN. 


ditions,  since  comparatively  smaller  doses  were  fatal  to  rabbits,  cats, 
and  dogs,  when  marked  lesions  not  due  to  caffein  were  found  at 
autopsy.     Glycosuria  was  observed  in  rabbits,  guinea  pigs,  and  cats     ■ 
when  caffein  was  given  in  sufficient  amounts.  ^ 

Table  18. — Acute   caffein   intoxication:   Table  showing  average  minimum  toxic  and 
minimum  fatal  doses  for  adult  animals. 


Effect  of 
dose. 

Dose  per  kilo  (grams.) 

Animal. 

Subeuta- 
neously. 

By  mouth. 

Intraper- 
itoneally. 

Intra- 
muscular. 

Intra- 
venous. 

/Toxic... 
\Fatal.... 

/Toxic . . . 

0.15 
.30 

0.325 
.350 

0. 100-0. 125 
.150 

0. 13-0. 15 
.20 

0.05 

0. 10-  .  16 

\Fatal.... 

/Toxic... 
\.Fatal.... 

/Toxic... 
\Fatal.... 

/Toxic . . . 

.20 

0. 15-  . 16 
.20-  .24 

.12-  .14 
.15 

.290 

.150 
0.280-  .300 

.125 
.150 

. 100-  .  120 
, 140-  .  150 

.200 
.240-  .250 

.  125-  .  160 
.180-  .200 

Cat 

" 

Dog.           

\Fatal.... 

.15-  .16 

Note. — The  doses  given  in  this  table  are  approximate. 


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